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PREPARE(7)                         PostgreSQL 14.23 Documentation                         PREPARE(7)



NAME
       PREPARE - prepare a statement for execution

SYNOPSIS
       PREPARE name [ ( data_type [, ...] ) ] AS statement

DESCRIPTION
       PREPARE creates a prepared statement. A prepared statement is a server-side object that can
       be used to optimize performance. When the PREPARE statement is executed, the specified
       statement is parsed, analyzed, and rewritten. When an EXECUTE command is subsequently issued,
       the prepared statement is planned and executed. This division of labor avoids repetitive
       parse analysis work, while allowing the execution plan to depend on the specific parameter
       values supplied.

       Prepared statements can take parameters: values that are substituted into the statement when
       it is executed. When creating the prepared statement, refer to parameters by position, using
       $1, $2, etc. A corresponding list of parameter data types can optionally be specified. When a
       parameter's data type is not specified or is declared as unknown, the type is inferred from
       the context in which the parameter is first referenced (if possible). When executing the
       statement, specify the actual values for these parameters in the EXECUTE statement. Refer to
       EXECUTE(7) for more information about that.

       Prepared statements only last for the duration of the current database session. When the
       session ends, the prepared statement is forgotten, so it must be recreated before being used
       again. This also means that a single prepared statement cannot be used by multiple
       simultaneous database clients; however, each client can create their own prepared statement
       to use. Prepared statements can be manually cleaned up using the DEALLOCATE command.

       Prepared statements potentially have the largest performance advantage when a single session
       is being used to execute a large number of similar statements. The performance difference
       will be particularly significant if the statements are complex to plan or rewrite, e.g., if
       the query involves a join of many tables or requires the application of several rules. If the
       statement is relatively simple to plan and rewrite but relatively expensive to execute, the
       performance advantage of prepared statements will be less noticeable.

PARAMETERS
       name
           An arbitrary name given to this particular prepared statement. It must be unique within a
           single session and is subsequently used to execute or deallocate a previously prepared
           statement.

       data_type
           The data type of a parameter to the prepared statement. If the data type of a particular
           parameter is unspecified or is specified as unknown, it will be inferred from the context
           in which the parameter is first referenced. To refer to the parameters in the prepared
           statement itself, use $1, $2, etc.

       statement
           Any SELECT, INSERT, UPDATE, DELETE, or VALUES statement.

NOTES
       A prepared statement can be executed with either a generic plan or a custom plan. A generic
       plan is the same across all executions, while a custom plan is generated for a specific
       execution using the parameter values given in that call. Use of a generic plan avoids
       planning overhead, but in some situations a custom plan will be much more efficient to
       execute because the planner can make use of knowledge of the parameter values. (Of course, if
       the prepared statement has no parameters, then this is moot and a generic plan is always
       used.)

       By default (that is, when plan_cache_mode is set to auto), the server will automatically
       choose whether to use a generic or custom plan for a prepared statement that has parameters.
       The current rule for this is that the first five executions are done with custom plans and
       the average estimated cost of those plans is calculated. Then a generic plan is created and
       its estimated cost is compared to the average custom-plan cost. Subsequent executions use the
       generic plan if its cost is not so much higher than the average custom-plan cost as to make
       repeated replanning seem preferable.

       This heuristic can be overridden, forcing the server to use either generic or custom plans,
       by setting plan_cache_mode to force_generic_plan or force_custom_plan respectively. This
       setting is primarily useful if the generic plan's cost estimate is badly off for some reason,
       allowing it to be chosen even though its actual cost is much more than that of a custom plan.

       To examine the query plan PostgreSQL is using for a prepared statement, use EXPLAIN, for
       example

           EXPLAIN EXECUTE name(parameter_values);

       If a generic plan is in use, it will contain parameter symbols $n, while a custom plan will
       have the supplied parameter values substituted into it.

       For more information on query planning and the statistics collected by PostgreSQL for that
       purpose, see the ANALYZE(7) documentation.

       Although the main point of a prepared statement is to avoid repeated parse analysis and
       planning of the statement, PostgreSQL will force re-analysis and re-planning of the statement
       before using it whenever database objects used in the statement have undergone definitional
       (DDL) changes or their planner statistics have been updated since the previous use of the
       prepared statement. Also, if the value of search_path changes from one use to the next, the
       statement will be re-parsed using the new search_path. (This latter behavior is new as of
       PostgreSQL 9.3.) These rules make use of a prepared statement semantically almost equivalent
       to re-submitting the same query text over and over, but with a performance benefit if no
       object definitions are changed, especially if the best plan remains the same across uses. An
       example of a case where the semantic equivalence is not perfect is that if the statement
       refers to a table by an unqualified name, and then a new table of the same name is created in
       a schema appearing earlier in the search_path, no automatic re-parse will occur since no
       object used in the statement changed. However, if some other change forces a re-parse, the
       new table will be referenced in subsequent uses.

       You can see all prepared statements available in the session by querying the
       pg_prepared_statements system view.

EXAMPLES
       Create a prepared statement for an INSERT statement, and then execute it:

           PREPARE fooplan (int, text, bool, numeric) AS
               INSERT INTO foo VALUES($1, $2, $3, $4);
           EXECUTE fooplan(1, 'Hunter Valley', 't', 200.00);

       Create a prepared statement for a SELECT statement, and then execute it:

           PREPARE usrrptplan (int) AS
               SELECT * FROM users u, logs l WHERE u.usrid=$1 AND u.usrid=l.usrid
               AND l.date = $2;
           EXECUTE usrrptplan(1, current_date);

       In this example, the data type of the second parameter is not specified, so it is inferred
       from the context in which $2 is used.

COMPATIBILITY
       The SQL standard includes a PREPARE statement, but it is only for use in embedded SQL. This
       version of the PREPARE statement also uses a somewhat different syntax.

SEE ALSO
       DEALLOCATE(7), EXECUTE(7)



PostgreSQL 14.23                                2026                                      PREPARE(7)