CREATE_TYPE(7) - man - phpman

CREATE TYPE(7)                     PostgreSQL 14.23 Documentation                     CREATE TYPE(7)



NAME
       CREATE_TYPE - define a new data type

SYNOPSIS
       CREATE TYPE name AS
           ( [ attribute_name data_type [ COLLATE collation ] [, ... ] ] )

       CREATE TYPE name AS ENUM
           ( [ 'label' [, ... ] ] )

       CREATE TYPE name AS RANGE (
           SUBTYPE = subtype
           [ , SUBTYPE_OPCLASS = subtype_operator_class ]
           [ , COLLATION = collation ]
           [ , CANONICAL = canonical_function ]
           [ , SUBTYPE_DIFF = subtype_diff_function ]
           [ , MULTIRANGE_TYPE_NAME = multirange_type_name ]
       )

       CREATE TYPE name (
           INPUT = input_function,
           OUTPUT = output_function
           [ , RECEIVE = receive_function ]
           [ , SEND = send_function ]
           [ , TYPMOD_IN = type_modifier_input_function ]
           [ , TYPMOD_OUT = type_modifier_output_function ]
           [ , ANALYZE = analyze_function ]
           [ , SUBSCRIPT = subscript_function ]
           [ , INTERNALLENGTH = { internallength | VARIABLE } ]
           [ , PASSEDBYVALUE ]
           [ , ALIGNMENT = alignment ]
           [ , STORAGE = storage ]
           [ , LIKE = like_type ]
           [ , CATEGORY = category ]
           [ , PREFERRED = preferred ]
           [ , DEFAULT = default ]
           [ , ELEMENT = element ]
           [ , DELIMITER = delimiter ]
           [ , COLLATABLE = collatable ]
       )

       CREATE TYPE name

DESCRIPTION
       CREATE TYPE registers a new data type for use in the current database. The user who defines a
       type becomes its owner.

       If a schema name is given then the type is created in the specified schema. Otherwise it is
       created in the current schema. The type name must be distinct from the name of any existing
       type or domain in the same schema. (Because tables have associated data types, the type name
       must also be distinct from the name of any existing table in the same schema.)

       There are five forms of CREATE TYPE, as shown in the syntax synopsis above. They respectively
       create a composite type, an enum type, a range type, a base type, or a shell type. The first
       four of these are discussed in turn below. A shell type is simply a placeholder for a type to
       be defined later; it is created by issuing CREATE TYPE with no parameters except for the type
       name. Shell types are needed as forward references when creating range types and base types,
       as discussed in those sections.

   Composite Types
       The first form of CREATE TYPE creates a composite type. The composite type is specified by a
       list of attribute names and data types. An attribute's collation can be specified too, if its
       data type is collatable. A composite type is essentially the same as the row type of a table,
       but using CREATE TYPE avoids the need to create an actual table when all that is wanted is to
       define a type. A stand-alone composite type is useful, for example, as the argument or return
       type of a function.

       To be able to create a composite type, you must have USAGE privilege on all attribute types.

   Enumerated Types
       The second form of CREATE TYPE creates an enumerated (enum) type, as described in
       Section 8.7. Enum types take a list of quoted labels, each of which must be less than
       NAMEDATALEN bytes long (64 bytes in a standard PostgreSQL build). (It is possible to create
       an enumerated type with zero labels, but such a type cannot be used to hold values before at
       least one label is added using ALTER TYPE.)

   Range Types
       The third form of CREATE TYPE creates a new range type, as described in Section 8.17.

       The range type's subtype can be any type with an associated b-tree operator class (to
       determine the ordering of values for the range type). Normally the subtype's default b-tree
       operator class is used to determine ordering; to use a non-default operator class, specify
       its name with subtype_opclass. If the subtype is collatable, and you want to use a
       non-default collation in the range's ordering, specify the desired collation with the
       collation option.

       The optional canonical function must take one argument of the range type being defined, and
       return a value of the same type. This is used to convert range values to a canonical form,
       when applicable. See Section 8.17.8 for more information. Creating a canonical function is a
       bit tricky, since it must be defined before the range type can be declared. To do this, you
       must first create a shell type, which is a placeholder type that has no properties except a
       name and an owner. This is done by issuing the command CREATE TYPE name, with no additional
       parameters. Then the function can be declared using the shell type as argument and result,
       and finally the range type can be declared using the same name. This automatically replaces
       the shell type entry with a valid range type.

       The optional subtype_diff function must take two values of the subtype type as argument, and
       return a double precision value representing the difference between the two given values.
       While this is optional, providing it allows much greater efficiency of GiST indexes on
       columns of the range type. See Section 8.17.8 for more information.

       The optional multirange_type_name parameter specifies the name of the corresponding
       multirange type. If not specified, this name is chosen automatically as follows. If the range
       type name contains the substring range, then the multirange type name is formed by
       replacement of the range substring with multirange in the range type name. Otherwise, the
       multirange type name is formed by appending a _multirange suffix to the range type name.

   Base Types
       The fourth form of CREATE TYPE creates a new base type (scalar type). To create a new base
       type, you must be a superuser. (This restriction is made because an erroneous type definition
       could confuse or even crash the server.)

       The parameters can appear in any order, not only that illustrated above, and most are
       optional. You must register two or more functions (using CREATE FUNCTION) before defining the
       type. The support functions input_function and output_function are required, while the
       functions receive_function, send_function, type_modifier_input_function,
       type_modifier_output_function, analyze_function, and subscript_function are optional.
       Generally these functions have to be coded in C or another low-level language.

       The input_function converts the type's external textual representation to the internal
       representation used by the operators and functions defined for the type.  output_function
       performs the reverse transformation. The input function can be declared as taking one
       argument of type cstring, or as taking three arguments of types cstring, oid, integer. The
       first argument is the input text as a C string, the second argument is the type's own OID
       (except for array types, which instead receive their element type's OID), and the third is
       the typmod of the destination column, if known (-1 will be passed if not). The input function
       must return a value of the data type itself. Usually, an input function should be declared
       STRICT; if it is not, it will be called with a NULL first parameter when reading a NULL input
       value. The function must still return NULL in this case, unless it raises an error. (This
       case is mainly meant to support domain input functions, which might need to reject NULL
       inputs.) The output function must be declared as taking one argument of the new data type.
       The output function must return type cstring. Output functions are not invoked for NULL
       values.

       The optional receive_function converts the type's external binary representation to the
       internal representation. If this function is not supplied, the type cannot participate in
       binary input. The binary representation should be chosen to be cheap to convert to internal
       form, while being reasonably portable. (For example, the standard integer data types use
       network byte order as the external binary representation, while the internal representation
       is in the machine's native byte order.) The receive function should perform adequate checking
       to ensure that the value is valid. The receive function can be declared as taking one
       argument of type internal, or as taking three arguments of types internal, oid, integer. The
       first argument is a pointer to a StringInfo buffer holding the received byte string; the
       optional arguments are the same as for the text input function. The receive function must
       return a value of the data type itself. Usually, a receive function should be declared
       STRICT; if it is not, it will be called with a NULL first parameter when reading a NULL input
       value. The function must still return NULL in this case, unless it raises an error. (This
       case is mainly meant to support domain receive functions, which might need to reject NULL
       inputs.) Similarly, the optional send_function converts from the internal representation to
       the external binary representation. If this function is not supplied, the type cannot
       participate in binary output. The send function must be declared as taking one argument of
       the new data type. The send function must return type bytea. Send functions are not invoked
       for NULL values.

       You should at this point be wondering how the input and output functions can be declared to
       have results or arguments of the new type, when they have to be created before the new type
       can be created. The answer is that the type should first be defined as a shell type, which is
       a placeholder type that has no properties except a name and an owner. This is done by issuing
       the command CREATE TYPE name, with no additional parameters. Then the C I/O functions can be
       defined referencing the shell type. Finally, CREATE TYPE with a full definition replaces the
       shell entry with a complete, valid type definition, after which the new type can be used
       normally.

       The optional type_modifier_input_function and type_modifier_output_function are needed if the
       type supports modifiers, that is optional constraints attached to a type declaration, such as
       char(5) or numeric(30,2).  PostgreSQL allows user-defined types to take one or more simple
       constants or identifiers as modifiers. However, this information must be capable of being
       packed into a single non-negative integer value for storage in the system catalogs. The
       type_modifier_input_function is passed the declared modifier(s) in the form of a cstring
       array. It must check the values for validity (throwing an error if they are wrong), and if
       they are correct, return a single non-negative integer value that will be stored as the
       column “typmod”. Type modifiers will be rejected if the type does not have a
       type_modifier_input_function. The type_modifier_output_function converts the internal integer
       typmod value back to the correct form for user display. It must return a cstring value that
       is the exact string to append to the type name; for example numeric's function might return
       (30,2). It is allowed to omit the type_modifier_output_function, in which case the default
       display format is just the stored typmod integer value enclosed in parentheses.

       The optional analyze_function performs type-specific statistics collection for columns of the
       data type. By default, ANALYZE will attempt to gather statistics using the type's “equals”
       and “less-than” operators, if there is a default b-tree operator class for the type. For
       non-scalar types this behavior is likely to be unsuitable, so it can be overridden by
       specifying a custom analysis function. The analysis function must be declared to take a
       single argument of type internal, and return a boolean result. The detailed API for analysis
       functions appears in src/include/commands/vacuum.h.

       The optional subscript_function allows the data type to be subscripted in SQL commands.
       Specifying this function does not cause the type to be considered a “true” array type; for
       example, it will not be a candidate for the result type of ARRAY[] constructs. But if
       subscripting a value of the type is a natural notation for extracting data from it, then a
       subscript_function can be written to define what that means. The subscript function must be
       declared to take a single argument of type internal, and return an internal result, which is
       a pointer to a struct of methods (functions) that implement subscripting. The detailed API
       for subscript functions appears in src/include/nodes/subscripting.h. It may also be useful to
       read the array implementation in src/backend/utils/adt/arraysubs.c, or the simpler code in
       contrib/hstore/hstore_subs.c. Additional information appears in Array Types below.

       While the details of the new type's internal representation are only known to the I/O
       functions and other functions you create to work with the type, there are several properties
       of the internal representation that must be declared to PostgreSQL. Foremost of these is
       internallength. Base data types can be fixed-length, in which case internallength is a
       positive integer, or variable-length, indicated by setting internallength to VARIABLE.
       (Internally, this is represented by setting typlen to -1.) The internal representation of all
       variable-length types must start with a 4-byte integer giving the total length of this value
       of the type. (Note that the length field is often encoded, as described in Section 70.2; it's
       unwise to access it directly.)

       The optional flag PASSEDBYVALUE indicates that values of this data type are passed by value,
       rather than by reference. Types passed by value must be fixed-length, and their internal
       representation cannot be larger than the size of the Datum type (4 bytes on some machines, 8
       bytes on others).

       The alignment parameter specifies the storage alignment required for the data type. The
       allowed values equate to alignment on 1, 2, 4, or 8 byte boundaries. Note that
       variable-length types must have an alignment of at least 4, since they necessarily contain an
       int4 as their first component.

       The storage parameter allows selection of storage strategies for variable-length data types.
       (Only plain is allowed for fixed-length types.)  plain specifies that data of the type will
       always be stored in-line and not compressed.  extended specifies that the system will first
       try to compress a long data value, and will move the value out of the main table row if it's
       still too long.  external allows the value to be moved out of the main table, but the system
       will not try to compress it.  main allows compression, but discourages moving the value out
       of the main table. (Data items with this storage strategy might still be moved out of the
       main table if there is no other way to make a row fit, but they will be kept in the main
       table preferentially over extended and external items.)

       All storage values other than plain imply that the functions of the data type can handle
       values that have been toasted, as described in Section 70.2 and Section 38.13.1. The specific
       other value given merely determines the default TOAST storage strategy for columns of a
       toastable data type; users can pick other strategies for individual columns using ALTER TABLE
       SET STORAGE.

       The like_type parameter provides an alternative method for specifying the basic
       representation properties of a data type: copy them from some existing type. The values of
       internallength, passedbyvalue, alignment, and storage are copied from the named type. (It is
       possible, though usually undesirable, to override some of these values by specifying them
       along with the LIKE clause.) Specifying representation this way is especially useful when the
       low-level implementation of the new type “piggybacks” on an existing type in some fashion.

       The category and preferred parameters can be used to help control which implicit cast will be
       applied in ambiguous situations. Each data type belongs to a category named by a single ASCII
       character, and each type is either “preferred” or not within its category. The parser will
       prefer casting to preferred types (but only from other types within the same category) when
       this rule is helpful in resolving overloaded functions or operators. For more details see
       Chapter 10. For types that have no implicit casts to or from any other types, it is
       sufficient to leave these settings at the defaults. However, for a group of related types
       that have implicit casts, it is often helpful to mark them all as belonging to a category and
       select one or two of the “most general” types as being preferred within the category. The
       category parameter is especially useful when adding a user-defined type to an existing
       built-in category, such as the numeric or string types. However, it is also possible to
       create new entirely-user-defined type categories. Select any ASCII character other than an
       upper-case letter to name such a category.

       A default value can be specified, in case a user wants columns of the data type to default to
       something other than the null value. Specify the default with the DEFAULT key word. (Such a
       default can be overridden by an explicit DEFAULT clause attached to a particular column.)

       To indicate that a type is a fixed-length array type, specify the type of the array elements
       using the ELEMENT key word. For example, to define an array of 4-byte integers (int4),
       specify ELEMENT = int4. For more details, see Array Types below.

       To indicate the delimiter to be used between values in the external representation of arrays
       of this type, delimiter can be set to a specific character. The default delimiter is the
       comma (,). Note that the delimiter is associated with the array element type, not the array
       type itself.

       If the optional Boolean parameter collatable is true, column definitions and expressions of
       the type may carry collation information through use of the COLLATE clause. It is up to the
       implementations of the functions operating on the type to actually make use of the collation
       information; this does not happen automatically merely by marking the type collatable.

   Array Types
       Whenever a user-defined type is created, PostgreSQL automatically creates an associated array
       type, whose name consists of the element type's name prepended with an underscore, and
       truncated if necessary to keep it less than NAMEDATALEN bytes long. (If the name so generated
       collides with an existing type name, the process is repeated until a non-colliding name is
       found.) This implicitly-created array type is variable length and uses the built-in input and
       output functions array_in and array_out. Furthermore, this type is what the system uses for
       constructs such as ARRAY[] over the user-defined type. The array type tracks any changes in
       its element type's owner or schema, and is dropped if the element type is.

       You might reasonably ask why there is an ELEMENT option, if the system makes the correct
       array type automatically. The main case where it's useful to use ELEMENT is when you are
       making a fixed-length type that happens to be internally an array of a number of identical
       things, and you want to allow these things to be accessed directly by subscripting, in
       addition to whatever operations you plan to provide for the type as a whole. For example,
       type point is represented as just two floating-point numbers, which can be accessed using
       point[0] and point[1]. Note that this facility only works for fixed-length types whose
       internal form is exactly a sequence of identical fixed-length fields. For historical reasons
       (i.e., this is clearly wrong but it's far too late to change it), subscripting of
       fixed-length array types starts from zero, rather than from one as for variable-length
       arrays.

       Specifying the SUBSCRIPT option allows a data type to be subscripted, even though the system
       does not otherwise regard it as an array type. The behavior just described for fixed-length
       arrays is actually implemented by the SUBSCRIPT handler function raw_array_subscript_handler,
       which is used automatically if you specify ELEMENT for a fixed-length type without also
       writing SUBSCRIPT.

       When specifying a custom SUBSCRIPT function, it is not necessary to specify ELEMENT unless
       the SUBSCRIPT handler function needs to consult typelem to find out what to return. Be aware
       that specifying ELEMENT causes the system to assume that the new type contains, or is somehow
       physically dependent on, the element type; thus for example changing properties of the
       element type won't be allowed if there are any columns of the dependent type.

PARAMETERS
       name
           The name (optionally schema-qualified) of a type to be created.

       attribute_name
           The name of an attribute (column) for the composite type.

       data_type
           The name of an existing data type to become a column of the composite type.

       collation
           The name of an existing collation to be associated with a column of a composite type, or
           with a range type.

       label
           A string literal representing the textual label associated with one value of an enum
           type.

       subtype
           The name of the element type that the range type will represent ranges of.

       subtype_operator_class
           The name of a b-tree operator class for the subtype.

       canonical_function
           The name of the canonicalization function for the range type.

       subtype_diff_function
           The name of a difference function for the subtype.

       multirange_type_name
           The name of the corresponding multirange type.

       input_function
           The name of a function that converts data from the type's external textual form to its
           internal form.

       output_function
           The name of a function that converts data from the type's internal form to its external
           textual form.

       receive_function
           The name of a function that converts data from the type's external binary form to its
           internal form.

       send_function
           The name of a function that converts data from the type's internal form to its external
           binary form.

       type_modifier_input_function
           The name of a function that converts an array of modifier(s) for the type into internal
           form.

       type_modifier_output_function
           The name of a function that converts the internal form of the type's modifier(s) to
           external textual form.

       analyze_function
           The name of a function that performs statistical analysis for the data type.

       subscript_function
           The name of a function that defines what subscripting a value of the data type does.

       internallength
           A numeric constant that specifies the length in bytes of the new type's internal
           representation. The default assumption is that it is variable-length.

       alignment
           The storage alignment requirement of the data type. If specified, it must be char, int2,
           int4, or double; the default is int4.

       storage
           The storage strategy for the data type. If specified, must be plain, external, extended,
           or main; the default is plain.

       like_type
           The name of an existing data type that the new type will have the same representation as.
           The values of internallength, passedbyvalue, alignment, and storage are copied from that
           type, unless overridden by explicit specification elsewhere in this CREATE TYPE command.

       category
           The category code (a single ASCII character) for this type. The default is 'U' for
           “user-defined type”. Other standard category codes can be found in Table 52.63. You may
           also choose other ASCII characters in order to create custom categories.

       preferred
           True if this type is a preferred type within its type category, else false. The default
           is false. Be very careful about creating a new preferred type within an existing type
           category, as this could cause surprising changes in behavior.

       default
           The default value for the data type. If this is omitted, the default is null.

       element
           The type being created is an array; this specifies the type of the array elements.

       delimiter
           The delimiter character to be used between values in arrays made of this type.

       collatable
           True if this type's operations can use collation information. The default is false.

NOTES
       Because there are no restrictions on use of a data type once it's been created, creating a
       base type or range type is tantamount to granting public execute permission on the functions
       mentioned in the type definition. This is usually not an issue for the sorts of functions
       that are useful in a type definition. But you might want to think twice before designing a
       type in a way that would require “secret” information to be used while converting it to or
       from external form.

       Before PostgreSQL version 8.3, the name of a generated array type was always exactly the
       element type's name with one underscore character (_) prepended. (Type names were therefore
       restricted in length to one fewer character than other names.) While this is still usually
       the case, the array type name may vary from this in case of maximum-length names or
       collisions with user type names that begin with underscore. Writing code that depends on this
       convention is therefore deprecated. Instead, use pg_type.typarray to locate the array type
       associated with a given type.

       It may be advisable to avoid using type and table names that begin with underscore. While the
       server will change generated array type names to avoid collisions with user-given names,
       there is still risk of confusion, particularly with old client software that may assume that
       type names beginning with underscores always represent arrays.

       Before PostgreSQL version 8.2, the shell-type creation syntax CREATE TYPE name did not exist.
       The way to create a new base type was to create its input function first. In this approach,
       PostgreSQL will first see the name of the new data type as the return type of the input
       function. The shell type is implicitly created in this situation, and then it can be
       referenced in the definitions of the remaining I/O functions. This approach still works, but
       is deprecated and might be disallowed in some future release. Also, to avoid accidentally
       cluttering the catalogs with shell types as a result of simple typos in function definitions,
       a shell type will only be made this way when the input function is written in C.

EXAMPLES
       This example creates a composite type and uses it in a function definition:

           CREATE TYPE compfoo AS (f1 int, f2 text);

           CREATE FUNCTION getfoo() RETURNS SETOF compfoo AS $$
               SELECT fooid, fooname FROM foo
           $$ LANGUAGE SQL;

       This example creates an enumerated type and uses it in a table definition:

           CREATE TYPE bug_status AS ENUM ('new', 'open', 'closed');

           CREATE TABLE bug (
               id serial,
               description text,
               status bug_status
           );

       This example creates a range type:

           CREATE TYPE float8_range AS RANGE (subtype = float8, subtype_diff = float8mi);

       This example creates the base data type box and then uses the type in a table definition:

           CREATE TYPE box;

           CREATE FUNCTION my_box_in_function(cstring) RETURNS box AS ... ;
           CREATE FUNCTION my_box_out_function(box) RETURNS cstring AS ... ;

           CREATE TYPE box (
               INTERNALLENGTH = 16,
               INPUT = my_box_in_function,
               OUTPUT = my_box_out_function
           );

           CREATE TABLE myboxes (
               id integer,
               description box
           );

       If the internal structure of box were an array of four float4 elements, we might instead use:

           CREATE TYPE box (
               INTERNALLENGTH = 16,
               INPUT = my_box_in_function,
               OUTPUT = my_box_out_function,
               ELEMENT = float4
           );

       which would allow a box value's component numbers to be accessed by subscripting. Otherwise
       the type behaves the same as before.

       This example creates a large object type and uses it in a table definition:

           CREATE TYPE bigobj (
               INPUT = lo_filein, OUTPUT = lo_fileout,
               INTERNALLENGTH = VARIABLE
           );
           CREATE TABLE big_objs (
               id integer,
               obj bigobj
           );

       More examples, including suitable input and output functions, are in Section 38.13.

COMPATIBILITY
       The first form of the CREATE TYPE command, which creates a composite type, conforms to the
       SQL standard. The other forms are PostgreSQL extensions. The CREATE TYPE statement in the SQL
       standard also defines other forms that are not implemented in PostgreSQL.

       The ability to create a composite type with zero attributes is a PostgreSQL-specific
       deviation from the standard (analogous to the same case in CREATE TABLE).

SEE ALSO
       ALTER TYPE (ALTER_TYPE(7)), CREATE DOMAIN (CREATE_DOMAIN(7)), CREATE FUNCTION
       (CREATE_FUNCTION(7)), DROP TYPE (DROP_TYPE(7))



PostgreSQL 14.23                                2026                                  CREATE TYPE(7)