DBD::SQLite - phpMan

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NAME SYNOPSIS DESCRIPTION SQLITE VERSION NOTABLE DIFFERENCES FROM OTHER DRIVERS DRIVER PRIVATE ATTRIBUTES METHODS DRIVER PRIVATE METHODS DRIVER FUNCTIONS DRIVER CONSTANTS COLLATION FUNCTIONS FULLTEXT SEARCH VIRTUAL TABLES IMPLEMENTED IN PERL TO DO SUPPORT AUTHORS COPYRIGHT
NAME
    DBD::SQLite - Self-contained RDBMS in a DBI Driver

SYNOPSIS
      use DBI;
      my $dbh = DBI->connect("dbi:SQLite:dbname=$dbfile","","");

DESCRIPTION
    SQLite is a public domain file-based relational database engine that you
    can find at <https://www.sqlite.org/>.

    DBD::SQLite is a Perl DBI driver for SQLite, that includes the entire
    thing in the distribution. So in order to get a fast transaction capable
    RDBMS working for your perl project you simply have to install this
    module, and nothing else.

    SQLite supports the following features:

    Implements a large subset of SQL92
        See <https://www.sqlite.org/lang.html> for details.

    A complete DB in a single disk file
        Everything for your database is stored in a single disk file, making
        it easier to move things around than with DBD::CSV.

    Atomic commit and rollback
        Yes, DBD::SQLite is small and light, but it supports full
        transactions!

    Extensible
        User-defined aggregate or regular functions can be registered with
        the SQL parser.

    There's lots more to it, so please refer to the docs on the SQLite web
    page, listed above, for SQL details. Also refer to DBI for details on
    how to use DBI itself. The API works like every DBI module does.
    However, currently many statement attributes are not implemented or are
    limited by the typeless nature of the SQLite database.

SQLITE VERSION
    DBD::SQLite is usually compiled with a bundled SQLite library (SQLite
    version 3.36.0 as of this release) for consistency. However, a different
    version of SQLite may sometimes be used for some reasons like security,
    or some new experimental features.

    You can look at $DBD::SQLite::sqlite_version ("3.x.y" format) or
    $DBD::SQLite::sqlite_version_number ("3xxxyyy" format) to find which
    version of SQLite is actually used. You can also check
    "DBD::SQLite::Constants::SQLITE_VERSION_NUMBER()".

    You can also find how the library is compiled by calling
    "DBD::SQLite::compile_options()" (see below).

NOTABLE DIFFERENCES FROM OTHER DRIVERS
  Database Name Is A File Name
    SQLite creates a file per a database. You should pass the "path" of the
    database file (with or without a parent directory) in the DBI connection
    string (as a database "name"):

      my $dbh = DBI->connect("dbi:SQLite:dbname=$dbfile","","");

    The file is opened in read/write mode, and will be created if it does
    not exist yet.

    Although the database is stored in a single file, the directory
    containing the database file must be writable by SQLite because the
    library will create several temporary files there.

    If the filename $dbfile is ":memory:", then a private, temporary
    in-memory database is created for the connection. This in-memory
    database will vanish when the database connection is closed. It is handy
    for your library tests.

    Note that future versions of SQLite might make use of additional special
    filenames that begin with the ":" character. It is recommended that when
    a database filename actually does begin with a ":" character you should
    prefix the filename with a pathname such as "./" to avoid ambiguity.

    If the filename $dbfile is an empty string, then a private, temporary
    on-disk database will be created. This private database will be
    automatically deleted as soon as the database connection is closed.

    As of 1.41_01, you can pass URI filename (see
    <https://www.sqlite.org/uri.html>) as well for finer control:

      my $dbh = DBI->connect("dbi:SQLite:uri=file:$path_to_dbfile?mode=rwc");

    Note that this is not for remote SQLite database connection. You can
    only connect to a local database.

  Read-Only Database
    You can set sqlite_open_flags (only) when you connect to a database:

      use DBD::SQLite::Constants qw/:file_open/;
      my $dbh = DBI->connect("dbi:SQLite:$dbfile", undef, undef, {
        sqlite_open_flags => SQLITE_OPEN_READONLY,
      });

    See <https://www.sqlite.org/c3ref/open.html> for details.

    As of 1.49_05, you can also make a database read-only by setting
    "ReadOnly" attribute to true (only) when you connect to a database.
    Actually you can set it after you connect, but in that case, it can't
    make the database read-only, and you'll see a warning (which you can
    hide by turning "PrintWarn" off).

  DBD::SQLite And File::Temp
    When you use File::Temp to create a temporary file/directory for SQLite
    databases, you need to remember:

    tempfile may be locked exclusively
        You may want to use "tempfile()" to create a temporary database
        filename for DBD::SQLite, but as noted in File::Temp's POD, this
        file may have an exclusive lock under some operating systems
        (notably Mac OSX), and result in a "database is locked" error. To
        avoid this, set EXLOCK option to false when you call tempfile().

          ($fh, $filename) = tempfile($template, EXLOCK => 0);

    CLEANUP may not work unless a database is disconnected
        When you set CLEANUP option to true when you create a temporary
        directory with "tempdir()" or "newdir()", you may have to disconnect
        databases explicitly before the temporary directory is gone (notably
        under MS Windows).

    (The above is quoted from the pod of File::Temp.)

    If you don't need to keep or share a temporary database, use ":memory:"
    database instead. It's much handier and cleaner for ordinary testing.

  DBD::SQLite and fork()
    Follow the advice in the SQLite FAQ (<https://sqlite.org/faq.html>).

        Under Unix, you should not carry an open SQLite database across a
        fork() system call into the child process. Problems will result if
        you do.

    You shouldn't (re)use a database handle you created (probably to set up
    a database schema etc) before you fork(). Otherwise, you might see a
    database corruption in the worst case.

    If you need to fork(), (re)open a database after you fork(). You might
    also want to tweak "sqlite_busy_timeout" and
    "sqlite_use_immediate_transaction" (see below), depending on your needs.

    If you need a higher level of concurrency than SQLite supports, consider
    using other client/server database engines.

  Accessing A Database With Other Tools
    To access the database from the command line, try using "dbish" which
    comes with the DBI::Shell module. Just type:

      dbish dbi:SQLite:foo.db

    On the command line to access the file foo.db.

    Alternatively you can install SQLite from the link above without
    conflicting with DBD::SQLite and use the supplied "sqlite3" command line
    tool.

  Blobs
    As of version 1.11, blobs should "just work" in SQLite as text columns.
    However this will cause the data to be treated as a string, so SQL
    statements such as length(x) will return the length of the column as a
    NUL terminated string, rather than the size of the blob in bytes. In
    order to store natively as a BLOB use the following code:

      use DBI qw(:sql_types);
      my $dbh = DBI->connect("dbi:SQLite:dbfile","","");

      my $blob = `cat foo.jpg`;
      my $sth = $dbh->prepare("INSERT INTO mytable VALUES (1, ?)");
      $sth->bind_param(1, $blob, SQL_BLOB);
      $sth->execute();

    And then retrieval just works:

      $sth = $dbh->prepare("SELECT * FROM mytable WHERE id = 1");
      $sth->execute();
      my $row = $sth->fetch;
      my $blobo = $row->[1];

      # now $blobo == $blob

  Functions And Bind Parameters
    As of this writing, a SQL that compares a return value of a function
    with a numeric bind value like this doesn't work as you might expect.

      my $sth = $dbh->prepare(q{
        SELECT bar FROM foo GROUP BY bar HAVING count(*) > ?;
      });
      $sth->execute(5);

    This is because DBD::SQLite assumes that all the bind values are text
    (and should be quoted) by default. Thus the above statement becomes like
    this while executing:

      SELECT bar FROM foo GROUP BY bar HAVING count(*) > "5";

    There are four workarounds for this.

    Use bind_param() explicitly
        As shown above in the "BLOB" section, you can always use
        "bind_param()" to tell the type of a bind value.

          use DBI qw(:sql_types);  # Don't forget this

          my $sth = $dbh->prepare(q{
            SELECT bar FROM foo GROUP BY bar HAVING count(*) > ?;
          });
          $sth->bind_param(1, 5, SQL_INTEGER);
          $sth->execute();

    Add zero to make it a number
        This is somewhat weird, but works anyway.

          my $sth = $dbh->prepare(q{
            SELECT bar FROM foo GROUP BY bar HAVING count(*) > (? + 0);
          });
          $sth->execute(5);

    Use SQL cast() function
        This is more explicit way to do the above.

          my $sth = $dbh->prepare(q{
            SELECT bar FROM foo GROUP BY bar HAVING count(*) > cast(? as integer);
          });
          $sth->execute(5);

    Set "sqlite_see_if_its_a_number" database handle attribute
        As of version 1.32_02, you can use "sqlite_see_if_its_a_number" to
        let DBD::SQLite to see if the bind values are numbers or not.

          $dbh->{sqlite_see_if_its_a_number} = 1;
          my $sth = $dbh->prepare(q{
            SELECT bar FROM foo GROUP BY bar HAVING count(*) > ?;
          });
          $sth->execute(5);

        You can set it to true when you connect to a database.

          my $dbh = DBI->connect('dbi:SQLite:foo', undef, undef, {
            AutoCommit => 1,
            RaiseError => 1,
            sqlite_see_if_its_a_number => 1,
          });

        This is the most straightforward solution, but as noted above,
        existing data in your databases created by DBD::SQLite have not
        always been stored as numbers, so this *might* cause other obscure
        problems. Use this sparingly when you handle existing databases. If
        you handle databases created by other tools like native "sqlite3"
        command line tool, this attribute would help you.

        As of 1.41_04, "sqlite_see_if_its_a_number" works only for bind
        values with no explicit type.

          my $dbh = DBI->connect('dbi:SQLite:foo', undef, undef, {
            AutoCommit => 1,
            RaiseError => 1,
            sqlite_see_if_its_a_number => 1,
          });
          my $sth = $dbh->prepare('INSERT INTO foo VALUES(?)');
          # '1.230' will be inserted as a text, instead of 1.23 as a number,
          # even though sqlite_see_if_its_a_number is set.
          $sth->bind_param(1, '1.230', SQL_VARCHAR);
          $sth->execute;

  Placeholders
    SQLite supports several placeholder expressions, including "?" and
    ":AAAA". Consult the DBI and SQLite documentation for details.

    <https://www.sqlite.org/lang_expr.html#varparam>

    Note that a question mark actually means a next unused (numbered)
    placeholder. You're advised not to use it with other (numbered or named)
    placeholders to avoid confusion.

      my $sth = $dbh->prepare(
        'update TABLE set a=?1 where b=?2 and a IS NOT ?1'
      );
      $sth->execute(1, 2);

  Pragma
    SQLite has a set of "Pragma"s to modify its operation or to query for
    its internal data. These are specific to SQLite and are not likely to
    work with other DBD libraries, but you may find some of these are quite
    useful, including:

    journal_mode
        You can use this pragma to change the journal mode for SQLite
        databases, maybe for better performance, or for compatibility.

        Its default mode is "DELETE", which means SQLite uses a rollback
        journal to implement transactions, and the journal is deleted at the
        conclusion of each transaction. If you use "TRUNCATE" instead of
        "DELETE", the journal will be truncated, which is usually much
        faster.

        A "WAL" (write-ahead log) mode is introduced as of SQLite 3.7.0.
        This mode is persistent, and it stays in effect even after closing
        and reopening the database. In other words, once the "WAL" mode is
        set in an application or in a test script, the database becomes
        inaccessible by older clients. This tends to be an issue when you
        use a system "sqlite3" executable under a conservative operating
        system.

        To fix this, You need to issue "PRAGMA journal_mode = DELETE" (or
        "TRUNCATE") beforehand, or install a newer version of "sqlite3".

    legacy_file_format
        If you happen to need to create a SQLite database that will also be
        accessed by a very old SQLite client (prior to 3.3.0 released in
        Jan. 2006), you need to set this pragma to ON before you create a
        database.

    reverse_unordered_selects
        You can set this pragma to ON to reverse the order of results of
        SELECT statements without an ORDER BY clause so that you can see if
        applications are making invalid assumptions about the result order.

        Note that SQLite 3.7.15 (bundled with DBD::SQLite 1.38_02) enhanced
        its query optimizer and the order of results of a SELECT statement
        without an ORDER BY clause may be different from the one of the
        previous versions.

    synchronous
        You can set set this pragma to OFF to make some of the operations in
        SQLite faster with a possible risk of database corruption in the
        worst case. See also "Performance" section below.

    See <https://www.sqlite.org/pragma.html> for more details.

  Foreign Keys
    SQLite has started supporting foreign key constraints since 3.6.19
    (released on Oct 14, 2009; bundled in DBD::SQLite 1.26_05). To be exact,
    SQLite has long been able to parse a schema with foreign keys, but the
    constraints has not been enforced. Now you can issue a "foreign_keys"
    pragma to enable this feature and enforce the constraints, preferably as
    soon as you connect to a database and you're not in a transaction:

      $dbh->do("PRAGMA foreign_keys = ON");

    And you can explicitly disable the feature whenever you like by turning
    the pragma off:

      $dbh->do("PRAGMA foreign_keys = OFF");

    As of this writing, this feature is disabled by default by the SQLite
    team, and by us, to secure backward compatibility, as this feature may
    break your applications, and actually broke some for us. If you have
    used a schema with foreign key constraints but haven't cared them much
    and supposed they're always ignored for SQLite, be prepared, and please
    do extensive testing to ensure that your applications will continue to
    work when the foreign keys support is enabled by default.

    See <https://www.sqlite.org/foreignkeys.html> for details.

  Transactions
    DBI/DBD::SQLite's transactions may be a bit confusing. They behave
    differently according to the status of the "AutoCommit" flag:

    When the AutoCommit flag is on
        You're supposed to always use the auto-commit mode, except you
        explicitly begin a transaction, and when the transaction ended,
        you're supposed to go back to the auto-commit mode. To begin a
        transaction, call "begin_work" method, or issue a "BEGIN" statement.
        To end it, call "commit/rollback" methods, or issue the
        corresponding statements.

          $dbh->{AutoCommit} = 1;

          $dbh->begin_work; # or $dbh->do('BEGIN TRANSACTION');

          # $dbh->{AutoCommit} is turned off temporarily during a transaction;

          $dbh->commit; # or $dbh->do('COMMIT');

          # $dbh->{AutoCommit} is turned on again;

    When the AutoCommit flag is off
        You're supposed to always use the transactional mode, until you
        explicitly turn on the AutoCommit flag. You can explicitly issue a
        "BEGIN" statement (only when an actual transaction has not begun
        yet) but you're not allowed to call "begin_work" method (if you
        don't issue a "BEGIN", it will be issued internally). You can commit
        or roll it back freely. Another transaction will automatically begin
        if you execute another statement.

          $dbh->{AutoCommit} = 0;

          # $dbh->do('BEGIN TRANSACTION') is not necessary, but possible

          ...

          $dbh->commit; # or $dbh->do('COMMIT');

          # $dbh->{AutoCommit} stays intact;

          $dbh->{AutoCommit} = 1;  # ends the transactional mode

    This "AutoCommit" mode is independent from the autocommit mode of the
    internal SQLite library, which always begins by a "BEGIN" statement, and
    ends by a "COMMIT" or a "ROLLBACK".

  Transaction and Database Locking
    The default transaction behavior of SQLite is "deferred", that means,
    locks are not acquired until the first read or write operation, and thus
    it is possible that another thread or process could create a separate
    transaction and write to the database after the "BEGIN" on the current
    thread has executed, and eventually cause a "deadlock". To avoid this,
    DBD::SQLite internally issues a "BEGIN IMMEDIATE" if you begin a
    transaction by calling "begin_work" or by turning off "AutoCommit"
    (since 1.38_01).

    If you really need to turn off this feature for some reasons, set
    "sqlite_use_immediate_transaction" database handle attribute to false,
    and the default "deferred" transaction will be used.

      my $dbh = DBI->connect("dbi:SQLite::memory:", "", "", {
        sqlite_use_immediate_transaction => 0,
      });

    Or, issue a "BEGIN" statement explicitly each time you begin a
    transaction.

    See <http://sqlite.org/lockingv3.html> for locking details.

  "$sth->finish" and Transaction Rollback
    As the DBI doc says, you almost certainly do not need to call "finish"
    in DBI method if you fetch all rows (probably in a loop). However, there
    are several exceptions to this rule, and rolling-back of an unfinished
    "SELECT" statement is one of such exceptional cases.

    SQLite prohibits "ROLLBACK" of unfinished "SELECT" statements in a
    transaction (See <http://sqlite.org/lang_transaction.html> for details).
    So you need to call "finish" before you issue a rollback.

      $sth = $dbh->prepare("SELECT * FROM t");
      $dbh->begin_work;
      eval {
          $sth->execute;
          $row = $sth->fetch;
          ...
          die "For some reason";
          ...
      };
      if($@) {
         $sth->finish;  # You need this for SQLite
         $dbh->rollback;
      } else {
         $dbh->commit;
      }

  Processing Multiple Statements At A Time
    DBI's statement handle is not supposed to process multiple statements at
    a time. So if you pass a string that contains multiple statements (a
    "dump") to a statement handle (via "prepare" or "do"), DBD::SQLite only
    processes the first statement, and discards the rest.

    If you need to process multiple statements at a time, set a
    "sqlite_allow_multiple_statements" attribute of a database handle to
    true when you connect to a database, and "do" method takes care of the
    rest (since 1.30_01, and without creating DBI's statement handles
    internally since 1.47_01). If you do need to use "prepare" or
    "prepare_cached" (which I don't recommend in this case, because
    typically there's no placeholder nor reusable part in a dump), you can
    look at "$sth->{sqlite_unprepared_statements}" to retrieve what's left,
    though it usually contains nothing but white spaces.

  TYPE statement attribute
    Because of historical reasons, DBD::SQLite's "TYPE" statement handle
    attribute returns an array ref of string values, contrary to the DBI
    specification. This value is also less useful for SQLite users because
    SQLite uses dynamic type system (that means, the datatype of a value is
    associated with the value itself, not with its container).

    As of version 1.61_02, if you set "sqlite_prefer_numeric_type" database
    handle attribute to true, "TYPE" statement handle attribute returns an
    array of integer, as an experiment.

  Performance
    SQLite is fast, very fast. Matt processed his 72MB log file with it,
    inserting the data (400,000+ rows) by using transactions and only
    committing every 1000 rows (otherwise the insertion is quite slow), and
    then performing queries on the data.

    Queries like count(*) and avg(bytes) took fractions of a second to
    return, but what surprised him most of all was:

      SELECT url, count(*) as count
      FROM access_log
      GROUP BY url
      ORDER BY count desc
      LIMIT 20

    To discover the top 20 hit URLs on the site (<http://axkit.org>), and it
    returned within 2 seconds. He was seriously considering switching his
    log analysis code to use this little speed demon!

    Oh yeah, and that was with no indexes on the table, on a 400MHz PIII.

    For best performance be sure to tune your hdparm settings if you are
    using linux. Also you might want to set:

      PRAGMA synchronous = OFF

    Which will prevent SQLite from doing fsync's when writing (which slows
    down non-transactional writes significantly) at the expense of some
    peace of mind. Also try playing with the cache_size pragma.

    The memory usage of SQLite can also be tuned using the cache_size
    pragma.

      $dbh->do("PRAGMA cache_size = 800000");

    The above will allocate 800M for DB cache; the default is 2M. Your sweet
    spot probably lies somewhere in between.

DRIVER PRIVATE ATTRIBUTES
  Database Handle Attributes
    sqlite_version
        Returns the version of the SQLite library which DBD::SQLite is
        using, e.g., "3.26.0". Can only be read.

    sqlite_string_mode
        SQLite strings are simple arrays of bytes, but Perl strings can
        store any arbitrary Unicode code point. Thus, DBD::SQLite has to
        adopt some method of translating between those two models. This
        parameter defines that translation.

        Accepted values are the following constants:

        *   DBD_SQLITE_STRING_MODE_BYTES: All strings are assumed to
            represent bytes. A Perl string that contains any code point
            above 255 will trigger an exception. This is appropriate for
            Latin-1 strings, binary data, pre-encoded UTF-8 strings, etc.

        *   DBD_SQLITE_STRING_MODE_UNICODE_FALLBACK: All Perl strings are
            encoded to UTF-8 before being given to SQLite. Perl will try to
            decode SQLite strings as UTF-8 when giving them to Perl. Should
            any such string not be valid UTF-8, a warning is thrown, and the
            string is left undecoded.

            This is appropriate for strings that are decoded to characters
            via, e.g., "decode" in Encode.

            Also note that, due to some bizarreness in SQLite's type system
            (see <https://www.sqlite.org/datatype3.html>), if you want to
            retain blob-style behavior for some columns under
            DBD_SQLITE_STRING_MODE_UNICODE_FALLBACK (say, to store images in
            the database), you have to state so explicitly using the
            3-argument form of "bind_param" in DBI when doing updates:

              use DBI qw(:sql_types);
              use DBD::SQLite::Constants ':dbd_sqlite_string_mode';
              $dbh->{sqlite_string_mode} = DBD_SQLITE_STRING_MODE_UNICODE_FALLBACK;
              my $sth = $dbh->prepare("INSERT INTO mytable (blobcolumn) VALUES (?)");

              # Binary_data will be stored as is.
              $sth->bind_param(1, $binary_data, SQL_BLOB);

            Defining the column type as "BLOB" in the DDL is not sufficient.

        *   DBD_SQLITE_STRING_MODE_UNICODE_STRICT: Like
            DBD_SQLITE_STRING_MODE_UNICODE_FALLBACK but usually throws an
            exception rather than a warning if SQLite sends invalid UTF-8.
            (In Perl callbacks from SQLite we still warn instead.)

        *   DBD_SQLITE_STRING_MODE_UNICODE_NAIVE: Like
            DBD_SQLITE_STRING_MODE_UNICODE_FALLBACK but uses a "naïve" UTF-8
            decoding method that forgoes validation. This is marginally
            faster than a validated decode, but it can also corrupt Perl
            itself!

        *   DBD_SQLITE_STRING_MODE_PV (default, but DO NOT USE): Like
            DBD_SQLITE_STRING_MODE_BYTES, but when translating Perl strings
            to SQLite the Perl string's internal byte buffer is given to
            SQLite. This is bad, but it's been the default for many years,
            and changing that would break existing applications.

    "sqlite_unicode" or "unicode" (deprecated)
        If truthy, equivalent to setting "sqlite_string_mode" to
        DBD_SQLITE_STRING_MODE_UNICODE_NAIVE; if falsy, equivalent to
        DBD_SQLITE_STRING_MODE_PV.

        Prefer "sqlite_string_mode" in all new code.

    sqlite_allow_multiple_statements
        If you set this to true, "do" method will process multiple
        statements at one go. This may be handy, but with performance
        penalty. See above for details.

    sqlite_use_immediate_transaction
        If you set this to true, DBD::SQLite tries to issue a "begin
        immediate transaction" (instead of "begin transaction") when
        necessary. See above for details.

        As of version 1.38_01, this attribute is set to true by default. If
        you really need to use "deferred" transactions for some reasons, set
        this to false explicitly.

    sqlite_see_if_its_a_number
        If you set this to true, DBD::SQLite tries to see if the bind values
        are number or not, and does not quote if they are numbers. See above
        for details.

    sqlite_extended_result_codes
        If set to true, DBD::SQLite uses extended result codes where
        appropriate (see <https://www.sqlite.org/rescode.html>).

    sqlite_defensive
        If set to true, language features that allow ordinary SQL to
        deliberately corrupt the database file are prohibited.

  Statement Handle Attributes
    sqlite_unprepared_statements
        Returns an unprepared part of the statement you pass to "prepare".
        Typically this contains nothing but white spaces after a semicolon.
        See above for details.

METHODS
    See also to the DBI documentation for the details of other common
    methods.

  table_info
      $sth = $dbh->table_info(undef, $schema, $table, $type, \%attr);

    Returns all tables and schemas (databases) as specified in "table_info"
    in DBI. The schema and table arguments will do a "LIKE" search. You can
    specify an ESCAPE character by including an 'Escape' attribute in
    \%attr. The $type argument accepts a comma separated list of the
    following types 'TABLE', 'VIEW', 'LOCAL TEMPORARY' and 'SYSTEM TABLE'
    (by default all are returned). Note that a statement handle is returned,
    and not a direct list of tables.

    The following fields are returned:

    TABLE_CAT: Always NULL, as SQLite does not have the concept of catalogs.

    TABLE_SCHEM: The name of the schema (database) that the table or view is
    in. The default schema is 'main', temporary tables are in 'temp' and
    other databases will be in the name given when the database was
    attached.

    TABLE_NAME: The name of the table or view.

    TABLE_TYPE: The type of object returned. Will be one of 'TABLE', 'VIEW',
    'LOCAL TEMPORARY' or 'SYSTEM TABLE'.

  primary_key, primary_key_info
      @names = $dbh->primary_key(undef, $schema, $table);
      $sth   = $dbh->primary_key_info(undef, $schema, $table, \%attr);

    You can retrieve primary key names or more detailed information. As
    noted above, SQLite does not have the concept of catalogs, so the first
    argument of the methods is usually "undef", and you'll usually set
    "undef" for the second one (unless you want to know the primary keys of
    temporary tables).

  foreign_key_info
      $sth = $dbh->foreign_key_info(undef, $pk_schema, $pk_table,
                                    undef, $fk_schema, $fk_table);

    Returns information about foreign key constraints, as specified in
    "foreign_key_info" in DBI, but with some limitations :

    *   information in rows returned by the $sth is incomplete with respect
        to the "foreign_key_info" in DBI specification. All requested fields
        are present, but the content is "undef" for some of them.

    The following nonempty fields are returned :

    PKTABLE_NAME: The primary (unique) key table identifier.

    PKCOLUMN_NAME: The primary (unique) key column identifier.

    FKTABLE_NAME: The foreign key table identifier.

    FKCOLUMN_NAME: The foreign key column identifier.

    KEY_SEQ: The column sequence number (starting with 1), when several
    columns belong to a same constraint.

    UPDATE_RULE: The referential action for the UPDATE rule. The following
    codes are defined:

      CASCADE              0
      RESTRICT             1
      SET NULL             2
      NO ACTION            3
      SET DEFAULT          4

    Default is 3 ('NO ACTION').

    DELETE_RULE: The referential action for the DELETE rule. The codes are
    the same as for UPDATE_RULE.

    DEFERRABILITY: The following codes are defined:

      INITIALLY DEFERRED   5
      INITIALLY IMMEDIATE  6
      NOT DEFERRABLE       7

    UNIQUE_OR_PRIMARY: Whether the column is primary or unique.

    Note: foreign key support in SQLite must be explicitly turned on through
    a "PRAGMA" command; see "Foreign keys" earlier in this manual.

  statistics_info
      $sth = $dbh->statistics_info(undef, $schema, $table,
                                    $unique_only, $quick);

    Returns information about a table and it's indexes, as specified in
    "statistics_info" in DBI, but with some limitations :

    *   information in rows returned by the $sth is incomplete with respect
        to the "statistics_info" in DBI specification. All requested fields
        are present, but the content is "undef" for some of them.

    The following nonempty fields are returned :

    TABLE_SCHEM: The name of the schema (database) that the table is in. The
    default schema is 'main', temporary tables are in 'temp' and other
    databases will be in the name given when the database was attached.

    TABLE_NAME: The name of the table

    NON_UNIQUE: Contains 0 for unique indexes, 1 for non-unique indexes

    INDEX_NAME: The name of the index

    TYPE: SQLite uses 'btree' for all it's indexes

    ORDINAL_POSITION: Column sequence number (starting with 1).

    COLUMN_NAME: The name of the column

  ping
      my $bool = $dbh->ping;

    returns true if the database file exists (or the database is in-memory),
    and the database connection is active.

DRIVER PRIVATE METHODS
    The following methods can be called via the func() method with a little
    tweak, but the use of func() method is now discouraged by the DBI author
    for various reasons (see DBI's document
    <https://metacpan.org/pod/DBI::DBD#Using-install_method()-to-expose-driv
    er-private-methods> for details). So, if you're using DBI >= 1.608, use
    these "sqlite_" methods. If you need to use an older DBI, you can call
    these like this:

      $dbh->func( ..., "(method name without sqlite_ prefix)" );

    Exception: "sqlite_trace" should always be called as is, even with
    "func()" method (to avoid conflict with DBI's trace() method).

      $dbh->func( ..., "sqlite_trace");

  $dbh->sqlite_last_insert_rowid()
    This method returns the last inserted rowid. If you specify an INTEGER
    PRIMARY KEY as the first column in your table, that is the column that
    is returned. Otherwise, it is the hidden ROWID column. See the SQLite
    docs for details.

    Generally you should not be using this method. Use the DBI
    last_insert_id method instead. The usage of this is:

      $h->last_insert_id($catalog, $schema, $table_name, $field_name [, \%attr ])

    Running "$h->last_insert_id("","","","")" is the equivalent of running
    "$dbh->sqlite_last_insert_rowid()" directly.

  $dbh->sqlite_db_filename()
    Retrieve the current (main) database filename. If the database is
    in-memory or temporary, this returns an empty string, or "undef".

  $dbh->sqlite_busy_timeout()
    Retrieve the current busy timeout.

  $dbh->sqlite_busy_timeout( $ms )
    Set the current busy timeout. The timeout is in milliseconds.

  $dbh->sqlite_create_function( $name, $argc, $code_ref, $flags )
    This method will register a new function which will be usable in an SQL
    query. The method's parameters are:

    $name
        The name of the function. This is the name of the function as it
        will be used from SQL.

    $argc
        The number of arguments taken by the function. If this number is -1,
        the function can take any number of arguments.

    $code_ref
        This should be a reference to the function's implementation.

    $flags
        You can optionally pass an extra flag bit to create_function, which
        then would be ORed with SQLITE_UTF8 (default). As of 1.47_02 (SQLite
        3.8.9), only meaning bit is SQLITE_DETERMINISTIC (introduced at
        SQLite 3.8.3), which can make the function perform better. See C API
        documentation at <http://sqlite.org/c3ref/create_function.html> for
        details.

    For example, here is how to define a now() function which returns the
    current number of seconds since the epoch:

      $dbh->sqlite_create_function( 'now', 0, sub { return time } );

    After this, it could be used from SQL as:

      INSERT INTO mytable ( now() );

    The function should return a scalar value, and the value is treated as a
    text (or a number if appropriate) by default. If you do need to specify
    a type of the return value (like BLOB), you can return a reference to an
    array that contains the value and the type, as of 1.65_01.

      $dbh->sqlite_create_function( 'md5', 1, sub { return [md5($_[0]), SQL_BLOB] } );

   REGEXP function
    SQLite includes syntactic support for an infix operator 'REGEXP', but
    without any implementation. The "DBD::SQLite" driver automatically
    registers an implementation that performs standard perl regular
    expression matching, using current locale. So for example you can search
    for words starting with an 'A' with a query like

      SELECT * from table WHERE column REGEXP '\bA\w+'

    If you want case-insensitive searching, use perl regex flags, like this
    :

      SELECT * from table WHERE column REGEXP '(?i:\bA\w+)'

    The default REGEXP implementation can be overridden through the
    "create_function" API described above.

    Note that regexp matching will not use SQLite indices, but will iterate
    over all rows, so it could be quite costly in terms of performance.

  $dbh->sqlite_create_collation( $name, $code_ref )
    This method manually registers a new function which will be usable in an
    SQL query as a COLLATE option for sorting. Such functions can also be
    registered automatically on demand: see section "COLLATION FUNCTIONS"
    below.

    The method's parameters are:

    $name
        The name of the function exposed to SQL.

    $code_ref
        Reference to the function's implementation. The driver will check
        that this is a proper sorting function.

  $dbh->sqlite_collation_needed( $code_ref )
    This method manually registers a callback function that will be invoked
    whenever an undefined collation sequence is required from an SQL
    statement. The callback is invoked as

      $code_ref->($dbh, $collation_name)

    and should register the desired collation using
    "sqlite_create_collation".

    An initial callback is already registered by "DBD::SQLite", so for most
    common cases it will be simpler to just add your collation sequences in
    the %DBD::SQLite::COLLATION hash (see section "COLLATION FUNCTIONS"
    below).

  $dbh->sqlite_create_aggregate( $name, $argc, $pkg, $flags )
    This method will register a new aggregate function which can then be
    used from SQL. The method's parameters are:

    $name
        The name of the aggregate function, this is the name under which the
        function will be available from SQL.

    $argc
        This is an integer which tells the SQL parser how many arguments the
        function takes. If that number is -1, the function can take any
        number of arguments.

    $pkg
        This is the package which implements the aggregator interface.

    $flags
        You can optionally pass an extra flag bit to create_aggregate, which
        then would be ORed with SQLITE_UTF8 (default). As of 1.47_02 (SQLite
        3.8.9), only meaning bit is SQLITE_DETERMINISTIC (introduced at
        SQLite 3.8.3), which can make the function perform better. See C API
        documentation at <http://sqlite.org/c3ref/create_function.html> for
        details.

    The aggregator interface consists of defining three methods:

    new()
        This method will be called once to create an object which should be
        used to aggregate the rows in a particular group. The step() and
        finalize() methods will be called upon the reference return by the
        method.

    step(@_)
        This method will be called once for each row in the aggregate.

    finalize()
        This method will be called once all rows in the aggregate were
        processed and it should return the aggregate function's result. When
        there is no rows in the aggregate, finalize() will be called right
        after new().

    Here is a simple aggregate function which returns the variance (example
    adapted from pysqlite):

      package variance;

      sub new { bless [], shift; }

      sub step {
          my ( $self, $value ) = @_;

          push @$self, $value;
      }

      sub finalize {
          my $self = $_[0];

          my $n = @$self;

          # Variance is NULL unless there is more than one row
          return undef unless $n || $n == 1;

          my $mu = 0;
          foreach my $v ( @$self ) {
              $mu += $v;
          }
          $mu /= $n;

          my $sigma = 0;
          foreach my $v ( @$self ) {
              $sigma += ($v - $mu)**2;
          }
          $sigma = $sigma / ($n - 1);

          return $sigma;
      }

      $dbh->sqlite_create_aggregate( "variance", 1, 'variance' );

    The aggregate function can then be used as:

      SELECT group_name, variance(score)
      FROM results
      GROUP BY group_name;

    For more examples, see the DBD::SQLite::Cookbook.

  $dbh->sqlite_progress_handler( $n_opcodes, $code_ref )
    This method registers a handler to be invoked periodically during long
    running calls to SQLite.

    An example use for this interface is to keep a GUI updated during a
    large query. The parameters are:

    $n_opcodes
        The progress handler is invoked once for every $n_opcodes virtual
        machine opcodes in SQLite.

    $code_ref
        Reference to the handler subroutine. If the progress handler returns
        non-zero, the SQLite operation is interrupted. This feature can be
        used to implement a "Cancel" button on a GUI dialog box.

        Set this argument to "undef" if you want to unregister a previous
        progress handler.

  $dbh->sqlite_commit_hook( $code_ref )
    This method registers a callback function to be invoked whenever a
    transaction is committed. Any callback set by a previous call to
    "sqlite_commit_hook" is overridden. A reference to the previous callback
    (if any) is returned. Registering an "undef" disables the callback.

    When the commit hook callback returns zero, the commit operation is
    allowed to continue normally. If the callback returns non-zero, then the
    commit is converted into a rollback (in that case, any attempt to
    *explicitly* call "$dbh->rollback()" afterwards would yield an error).

  $dbh->sqlite_rollback_hook( $code_ref )
    This method registers a callback function to be invoked whenever a
    transaction is rolled back. Any callback set by a previous call to
    "sqlite_rollback_hook" is overridden. A reference to the previous
    callback (if any) is returned. Registering an "undef" disables the
    callback.

  $dbh->sqlite_update_hook( $code_ref )
    This method registers a callback function to be invoked whenever a row
    is updated, inserted or deleted. Any callback set by a previous call to
    "sqlite_update_hook" is overridden. A reference to the previous callback
    (if any) is returned. Registering an "undef" disables the callback.

    The callback will be called as

      $code_ref->($action_code, $database, $table, $rowid)

    where

    $action_code
        is an integer equal to either "DBD::SQLite::INSERT",
        "DBD::SQLite::DELETE" or "DBD::SQLite::UPDATE" (see "Action Codes");

    $database
        is the name of the database containing the affected row;

    $table
        is the name of the table containing the affected row;

    $rowid
        is the unique 64-bit signed integer key of the affected row within
        that table.

  $dbh->sqlite_set_authorizer( $code_ref )
    This method registers an authorizer callback to be invoked whenever SQL
    statements are being compiled by the "prepare" in DBI method. The
    authorizer callback should return "DBD::SQLite::OK" to allow the action,
    "DBD::SQLite::IGNORE" to disallow the specific action but allow the SQL
    statement to continue to be compiled, or "DBD::SQLite::DENY" to cause
    the entire SQL statement to be rejected with an error. If the authorizer
    callback returns any other value, then "prepare" call that triggered the
    authorizer will fail with an error message.

    An authorizer is used when preparing SQL statements from an untrusted
    source, to ensure that the SQL statements do not try to access data they
    are not allowed to see, or that they do not try to execute malicious
    statements that damage the database. For example, an application may
    allow a user to enter arbitrary SQL queries for evaluation by a
    database. But the application does not want the user to be able to make
    arbitrary changes to the database. An authorizer could then be put in
    place while the user-entered SQL is being prepared that disallows
    everything except SELECT statements.

    The callback will be called as

      $code_ref->($action_code, $string1, $string2, $database, $trigger_or_view)

    where

    $action_code
        is an integer that specifies what action is being authorized (see
        "Action Codes").

    $string1, $string2
        are strings that depend on the action code (see "Action Codes").

    $database
        is the name of the database ("main", "temp", etc.) if applicable.

    $trigger_or_view
        is the name of the inner-most trigger or view that is responsible
        for the access attempt, or "undef" if this access attempt is
        directly from top-level SQL code.

  $dbh->sqlite_backup_from_file( $filename )
    This method accesses the SQLite Online Backup API, and will take a
    backup of the named database file, copying it to, and overwriting, your
    current database connection. This can be particularly handy if your
    current connection is to the special :memory: database, and you wish to
    populate it from an existing DB.

  $dbh->sqlite_backup_to_file( $filename )
    This method accesses the SQLite Online Backup API, and will take a
    backup of the currently connected database, and write it out to the
    named file.

  $dbh->sqlite_backup_from_dbh( $another_dbh )
    This method accesses the SQLite Online Backup API, and will take a
    backup of the database for the passed handle, copying it to, and
    overwriting, your current database connection. This can be particularly
    handy if your current connection is to the special :memory: database,
    and you wish to populate it from an existing DB. You can use this to
    backup from an in-memory database to another in-memory database.

  $dbh->sqlite_backup_to_dbh( $another_dbh )
    This method accesses the SQLite Online Backup API, and will take a
    backup of the currently connected database, and write it out to the
    passed database handle.

  $dbh->sqlite_enable_load_extension( $bool )
    Calling this method with a true value enables loading (external) SQLite3
    extensions. After the call, you can load extensions like this:

      $dbh->sqlite_enable_load_extension(1);
      $sth = $dbh->prepare("select load_extension('libsqlitefunctions.so')")
      or die "Cannot prepare: " . $dbh->errstr();

  $dbh->sqlite_load_extension( $file, $proc )
    Loading an extension by a select statement (with the "load_extension"
    SQLite3 function like above) has some limitations. If you need to, say,
    create other functions from an extension, use this method. $file (a path
    to the extension) is mandatory, and $proc (an entry point name) is
    optional. You need to call "sqlite_enable_load_extension" before calling
    "sqlite_load_extension".

    If the extension uses SQLite mutex functions like "sqlite3_mutex_enter",
    then the extension should be compiled with the same "SQLITE_THREADSAFE"
    compile-time setting as this module, see
    "DBD::SQLite::compile_options()".

  $dbh->sqlite_trace( $code_ref )
    This method registers a trace callback to be invoked whenever SQL
    statements are being run.

    The callback will be called as

      $code_ref->($statement)

    where

    $statement
        is a UTF-8 rendering of the SQL statement text as the statement
        first begins executing.

    Additional callbacks might occur as each triggered subprogram is
    entered. The callbacks for triggers contain a UTF-8 SQL comment that
    identifies the trigger.

    See also "TRACING" in DBI for better tracing options.

  $dbh->sqlite_profile( $code_ref )
    This method registers a profile callback to be invoked whenever a SQL
    statement finishes.

    The callback will be called as

      $code_ref->($statement, $elapsed_time)

    where

    $statement
        is the original statement text (without bind parameters).

    $elapsed_time
        is an estimate of wall-clock time of how long that statement took to
        run (in milliseconds).

    This method is considered experimental and is subject to change in
    future versions of SQLite.

    See also DBI::Profile for better profiling options.

  $dbh->sqlite_table_column_metadata( $dbname, $tablename, $columnname )
    is for internal use only.

  $dbh->sqlite_db_status()
    Returns a hash reference that holds a set of status information of
    database connection such as cache usage. See
    <https://www.sqlite.org/c3ref/c_dbstatus_options.html> for details. You
    may also pass 0 as an argument to reset the status.

  $sth->sqlite_st_status()
    Returns a hash reference that holds a set of status information of
    SQLite statement handle such as full table scan count. See
    <https://www.sqlite.org/c3ref/c_stmtstatus_counter.html> for details.
    Statement status only holds the current value.

      my $status = $sth->sqlite_st_status();
      my $cur = $status->{fullscan_step};

    You may also pass 0 as an argument to reset the status.

  $dbh->sqlite_db_config( $id, $new_integer_value )
    You can change how the connected database should behave like this:

      use DBD::SQLite::Constants qw/:database_connection_configuration_options/;

      my $dbh = DBI->connect('dbi:SQLite::memory:');

      # This disables language features that allow ordinary SQL
      # to deliberately corrupt the database file
      $dbh->sqlite_db_config( SQLITE_DBCONFIG_DEFENSIVE, 1 );

      # This disables two-arg version of fts3_tokenizer.
      $dbh->sqlite_db_config( SQLITE_DBCONFIG_ENABLE_FTS3_TOKENIZER, 0 );

    "sqlite_db_config" returns the new value after the call. If you just
    want to know the current value without changing anything, pass a
    negative integer value.

      my $current_value = $dbh->sqlite_db_config( SQLITE_DBCONFIG_DEFENSIVE, -1 );

    As of this writing, "sqlite_db_config" only supports options that set an
    integer value. "SQLITE_DBCONFIG_LOOKASIDE" and
    "SQLITE_DBCONFIG_MAINDBNAME" are not supported. See also
    "https://www.sqlite.org/capi3ref.html#sqlite3_db_config" for details.

  $dbh->sqlite_create_module()
    Registers a name for a *virtual table module*. Module names must be
    registered before creating a new virtual table using the module and
    before using a preexisting virtual table for the module. Virtual tables
    are explained in DBD::SQLite::VirtualTable.

  $dbh->sqlite_limit( $category_id, $new_value )
    Sets a new run-time limit for the category, and returns the current
    limit. If the new value is a negative number (or omitted), the limit is
    unchanged and just returns the current limit. Category ids
    (SQLITE_LIMIT_LENGTH, SQLITE_LIMIT_VARIABLE_NUMBER, etc) can be imported
    from DBD::SQLite::Constants.

  $dbh->sqlite_get_autocommit()
    Returns true if the internal SQLite connection is in an autocommit mode.
    This does not always return the same value as "$dbh->{AutoCommit}". This
    returns false if you explicitly issue a "<BEGIN"> statement.

  $dbh->sqlite_txn_state()
    Returns the internal transaction status of SQLite (not of DBI). Return
    values (SQLITE_TXN_NONE, SQLITE_TXN_READ, SQLITE_TXN_WRITE) can be
    imported from DBD::SQLite::Constants. You may pass an optional schema
    name (usually "main"). If SQLite does not support this function, or if
    you pass a wrong schema name, -1 is returned.

DRIVER FUNCTIONS
  DBD::SQLite::compile_options()
    Returns an array of compile options (available since SQLite 3.6.23,
    bundled in DBD::SQLite 1.30_01), or an empty array if the bundled
    library is old or compiled with SQLITE_OMIT_COMPILEOPTION_DIAGS.

  DBD::SQLite::sqlite_status()
    Returns a hash reference that holds a set of status information of
    SQLite runtime such as memory usage or page cache usage (see
    <https://www.sqlite.org/c3ref/c_status_malloc_count.html> for details).
    Each of the entry contains the current value and the highwater value.

      my $status = DBD::SQLite::sqlite_status();
      my $cur  = $status->{memory_used}{current};
      my $high = $status->{memory_used}{highwater};

    You may also pass 0 as an argument to reset the status.

  DBD::SQLite::strlike($pattern, $string, $escape_char), DBD::SQLite::strglob($pattern, $string)
    As of 1.49_05 (SQLite 3.10.0), you can use these two functions to see if
    a string matches a pattern. These may be useful when you create a
    virtual table or a custom function. See
    <http://sqlite.org/c3ref/strlike.html> and
    <http://sqlite.org/c3ref/strglob.html> for details.

DRIVER CONSTANTS
    A subset of SQLite C constants are made available to Perl, because they
    may be needed when writing hooks or authorizer callbacks. For accessing
    such constants, the "DBD::SQLite" module must be explicitly "use"d at
    compile time. For example, an authorizer that forbids any DELETE
    operation would be written as follows :

      use DBD::SQLite;
      $dbh->sqlite_set_authorizer(sub {
        my $action_code = shift;
        return $action_code == DBD::SQLite::DELETE ? DBD::SQLite::DENY
                                                   : DBD::SQLite::OK;
      });

    The list of constants implemented in "DBD::SQLite" is given below; more
    information can be found ad at
    <https://www.sqlite.org/c3ref/constlist.html>.

  Authorizer Return Codes
      OK
      DENY
      IGNORE

  Action Codes
    The "set_authorizer" method registers a callback function that is
    invoked to authorize certain SQL statement actions. The first parameter
    to the callback is an integer code that specifies what action is being
    authorized. The second and third parameters to the callback are strings,
    the meaning of which varies according to the action code. Below is the
    list of action codes, together with their associated strings.

      # constant              string1         string2
      # ========              =======         =======
      CREATE_INDEX            Index Name      Table Name
      CREATE_TABLE            Table Name      undef
      CREATE_TEMP_INDEX       Index Name      Table Name
      CREATE_TEMP_TABLE       Table Name      undef
      CREATE_TEMP_TRIGGER     Trigger Name    Table Name
      CREATE_TEMP_VIEW        View Name       undef
      CREATE_TRIGGER          Trigger Name    Table Name
      CREATE_VIEW             View Name       undef
      DELETE                  Table Name      undef
      DROP_INDEX              Index Name      Table Name
      DROP_TABLE              Table Name      undef
      DROP_TEMP_INDEX         Index Name      Table Name
      DROP_TEMP_TABLE         Table Name      undef
      DROP_TEMP_TRIGGER       Trigger Name    Table Name
      DROP_TEMP_VIEW          View Name       undef
      DROP_TRIGGER            Trigger Name    Table Name
      DROP_VIEW               View Name       undef
      INSERT                  Table Name      undef
      PRAGMA                  Pragma Name     1st arg or undef
      READ                    Table Name      Column Name
      SELECT                  undef           undef
      TRANSACTION             Operation       undef
      UPDATE                  Table Name      Column Name
      ATTACH                  Filename        undef
      DETACH                  Database Name   undef
      ALTER_TABLE             Database Name   Table Name
      REINDEX                 Index Name      undef
      ANALYZE                 Table Name      undef
      CREATE_VTABLE           Table Name      Module Name
      DROP_VTABLE             Table Name      Module Name
      FUNCTION                undef           Function Name
      SAVEPOINT               Operation       Savepoint Name

COLLATION FUNCTIONS
  Definition
    SQLite v3 provides the ability for users to supply arbitrary comparison
    functions, known as user-defined "collation sequences" or "collating
    functions", to be used for comparing two text values.
    <https://www.sqlite.org/datatype3.html#collation> explains how
    collations are used in various SQL expressions.

  Builtin collation sequences
    The following collation sequences are builtin within SQLite :

    BINARY
        Compares string data using memcmp(), regardless of text encoding.

    NOCASE
        The same as binary, except the 26 upper case characters of ASCII are
        folded to their lower case equivalents before the comparison is
        performed. Note that only ASCII characters are case folded. SQLite
        does not attempt to do full UTF case folding due to the size of the
        tables required.

    RTRIM
        The same as binary, except that trailing space characters are
        ignored.

    In addition, "DBD::SQLite" automatically installs the following
    collation sequences :

    perl
        corresponds to the Perl "cmp" operator

    perllocale
        Perl "cmp" operator, in a context where "use locale" is activated.

  Usage
    You can write for example

      CREATE TABLE foo(
          txt1 COLLATE perl,
          txt2 COLLATE perllocale,
          txt3 COLLATE nocase
      )

    or

      SELECT * FROM foo ORDER BY name COLLATE perllocale

  Unicode handling
    If the attribute "$dbh->{sqlite_unicode}" is set, strings coming from
    the database and passed to the collation function will be properly
    tagged with the utf8 flag; but this only works if the "sqlite_unicode"
    attribute is set before the first call to a perl collation sequence .
    The recommended way to activate unicode is to set the parameter at
    connection time :

      my $dbh = DBI->connect(
          "dbi:SQLite:dbname=foo", "", "",
          {
              RaiseError     => 1,
              sqlite_unicode => 1,
          }
      );

  Adding user-defined collations
    The native SQLite API for adding user-defined collations is exposed
    through methods "sqlite_create_collation" and "sqlite_collation_needed".

    To avoid calling these functions every time a $dbh handle is created,
    "DBD::SQLite" offers a simpler interface through the
    %DBD::SQLite::COLLATION hash : just insert your own collation functions
    in that hash, and whenever an unknown collation name is encountered in
    SQL, the appropriate collation function will be loaded on demand from
    the hash. For example, here is a way to sort text values regardless of
    their accented characters :

      use DBD::SQLite;
      $DBD::SQLite::COLLATION{no_accents} = sub {
        my ( $a, $b ) = map lc, @_;
        tr[����������������������������]
          [aaaaaacdeeeeiiiinoooooouuuuy] for $a, $b;
        $a cmp $b;
      };
      my $dbh  = DBI->connect("dbi:SQLite:dbname=dbfile");
      my $sql  = "SELECT ... FROM ... ORDER BY ... COLLATE no_accents");
      my $rows = $dbh->selectall_arrayref($sql);

    The builtin "perl" or "perllocale" collations are predefined in that
    same hash.

    The COLLATION hash is a global registry within the current process;
    hence there is a risk of undesired side-effects. Therefore, to prevent
    action at distance, the hash is implemented as a "write-only" hash, that
    will happily accept new entries, but will raise an exception if any
    attempt is made to override or delete a existing entry (including the
    builtin "perl" and "perllocale").

    If you really, really need to change or delete an entry, you can always
    grab the tied object underneath %DBD::SQLite::COLLATION --- but don't do
    that unless you really know what you are doing. Also observe that
    changes in the global hash will not modify existing collations in
    existing database handles: it will only affect new *requests* for
    collations. In other words, if you want to change the behaviour of a
    collation within an existing $dbh, you need to call the
    "create_collation" method directly.

FULLTEXT SEARCH
    SQLite is bundled with an extension module for full-text indexing.
    Tables with this feature enabled can be efficiently queried to find rows
    that contain one or more instances of some specified words, in any
    column, even if the table contains many large documents.

    Explanations for using this feature are provided in a separate document:
    see DBD::SQLite::Fulltext_search.

R* TREE SUPPORT
    The RTREE extension module within SQLite adds support for creating a
    R-Tree, a special index for range and multidimensional queries. This
    allows users to create tables that can be loaded with (as an example)
    geospatial data such as latitude/longitude coordinates for buildings
    within a city :

      CREATE VIRTUAL TABLE city_buildings USING rtree(
         id,               -- Integer primary key
         minLong, maxLong, -- Minimum and maximum longitude
         minLat, maxLat    -- Minimum and maximum latitude
      );

    then query which buildings overlap or are contained within a specified
    region:

      # IDs that are contained within query coordinates
      my $contained_sql = <<"";
      SELECT id FROM city_buildings
         WHERE  minLong >= ? AND maxLong <= ?
         AND    minLat  >= ? AND maxLat  <= ?

      # ... and those that overlap query coordinates
      my $overlap_sql = <<"";
      SELECT id FROM city_buildings
         WHERE    maxLong >= ? AND minLong <= ?
         AND      maxLat  >= ? AND minLat  <= ?

      my $contained = $dbh->selectcol_arrayref($contained_sql,undef,
                            $minLong, $maxLong, $minLat, $maxLat);

      my $overlapping = $dbh->selectcol_arrayref($overlap_sql,undef,
                            $minLong, $maxLong, $minLat, $maxLat);

    For more detail, please see the SQLite R-Tree page
    (<https://www.sqlite.org/rtree.html>). Note that custom R-Tree queries
    using callbacks, as mentioned in the prior link, have not been
    implemented yet.

VIRTUAL TABLES IMPLEMENTED IN PERL
    SQLite has a concept of "virtual tables" which look like regular tables
    but are implemented internally through specific functions. The fulltext
    or R* tree features described in the previous chapters are examples of
    such virtual tables, implemented in C code.

    "DBD::SQLite" also supports virtual tables implemented in *Perl code*:
    see DBD::SQLite::VirtualTable for using or implementing such virtual
    tables. These can have many interesting uses for joining regular DBMS
    data with some other kind of data within your Perl programs. Bundled
    with the present distribution are :

    *   DBD::SQLite::VirtualTable::FileContent : implements a virtual column
        that exposes file contents. This is especially useful in conjunction
        with a fulltext index; see DBD::SQLite::Fulltext_search.

    *   DBD::SQLite::VirtualTable::PerlData : binds to a Perl array within
        the Perl program. This can be used for simple import/export
        operations, for debugging purposes, for joining data from different
        sources, etc.

    Other Perl virtual tables may also be published separately on CPAN.

FOR DBD::SQLITE EXTENSION AUTHORS
    Since 1.30_01, you can retrieve the bundled SQLite C source and/or
    header like this:

      use File::ShareDir 'dist_dir';
      use File::Spec::Functions 'catfile';

      # the whole sqlite3.h header
      my $sqlite3_h = catfile(dist_dir('DBD-SQLite'), 'sqlite3.h');

      # or only a particular header, amalgamated in sqlite3.c
      my $what_i_want = 'parse.h';
      my $sqlite3_c = catfile(dist_dir('DBD-SQLite'), 'sqlite3.c');
      open my $fh, '<', $sqlite3_c or die $!;
      my $code = do { local $/; <$fh> };
      my ($parse_h) = $code =~ m{(
        /\*+[ ]Begin[ ]file[ ]$what_i_want[ ]\*+
        .+?
        /\*+[ ]End[ ]of[ ]$what_i_want[ ]\*+/
      )}sx;
      open my $out, '>', $what_i_want or die $!;
      print $out $parse_h;
      close $out;

    You usually want to use this in your extension's "Makefile.PL", and you
    may want to add DBD::SQLite to your extension's "CONFIGURE_REQUIRES" to
    ensure your extension users use the same C source/header they use to
    build DBD::SQLite itself (instead of the ones installed in their
    system).

TO DO
    The following items remain to be done.

  Leak Detection
    Implement one or more leak detection tests that only run during
    AUTOMATED_TESTING and RELEASE_TESTING and validate that none of the C
    code we work with leaks.

  Stream API for Blobs
    Reading/writing into blobs using "sqlite2_blob_open" /
    "sqlite2_blob_close".

  Support for custom callbacks for R-Tree queries
    Custom queries of a R-Tree index using a callback are possible with the
    SQLite C API (<https://www.sqlite.org/rtree.html>), so one could
    potentially use a callback that narrowed the result set down based on a
    specific need, such as querying for overlapping circles.

SUPPORT
    Bugs should be reported to GitHub issues:

    <https://github.com/DBD-SQLite/DBD-SQLite/issues>

    or via RT if you prefer:

    <http://rt.cpan.org/NoAuth/ReportBug.html?Queue=DBD-SQLite>

    Note that bugs of bundled SQLite library (i.e. bugs in "sqlite3.[ch]")
    should be reported to the SQLite developers at sqlite.org via their bug
    tracker or via their mailing list.

    The master repository is on GitHub:

    <https://github.com/DBD-SQLite/DBD-SQLite>.

    We also have a mailing list:

    <http://lists.scsys.co.uk/cgi-bin/mailman/listinfo/dbd-sqlite>

AUTHORS
    Matt Sergeant <matt AT sergeant.org>

    Francis J. Lacoste <flacoste AT logreport.org>

    Wolfgang Sourdeau <wolfgang AT logreport.org>

    Adam Kennedy <adamk AT cpan.org>

    Max Maischein <corion AT cpan.org>

    Laurent Dami <dami AT cpan.org>

    Kenichi Ishigaki <ishigaki AT cpan.org>

COPYRIGHT
    The bundled SQLite code in this distribution is Public Domain.

    DBD::SQLite is copyright 2002 - 2007 Matt Sergeant.

    Some parts copyright 2008 Francis J. Lacoste.

    Some parts copyright 2008 Wolfgang Sourdeau.

    Some parts copyright 2008 - 2013 Adam Kennedy.

    Some parts copyright 2009 - 2013 Kenichi Ishigaki.

    Some parts derived from DBD::SQLite::Amalgamation copyright 2008 Audrey
    Tang.

    This program is free software; you can redistribute it and/or modify it
    under the same terms as Perl itself.

    The full text of the license can be found in the LICENSE file included
    with this module.


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