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Synopsis

FUNCTION name ( [ parameter_name data_type [, ...] ] )
  RETURNS type
  [ LANGUAGE language]
  [ NOT? DETERMINISTIC ]
  [ RETURNS NULL ON NULL INPUT ]
  [ CALLED ON NULL INPUT ]
  [ SECURITY { DEFINER | INVOKER } ]
  [ COMMENT description]
  statements

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Description

Declare a SQL routine. The name of the routine. Inline routines can use a simple string. Catalog routines must qualify the name of the catalog and schema. The list of parameters is a comma-separated list of names parameter_name and data types data_type, see data type. An empty list, specified as () is also valid. The type value after the RETURNS keyword identifies the data type of the routine output. The optional LANGUAGE characteristic identifies the language used for the routine definition with language. Only SQL is supported. The optional DETERMINISTIC or NOT DETERMINISTIC characteristic declares that the routine is deterministic. This means that repeated routine calls with identical input parameters yield the same result. For SQL language routines, a routine is non-deterministic if it calls any non-deterministic routines and functions. By default, routines are assume to have a deterministic behavior. The optional RETURNS NULL ON NULL INPUT characteristic declares that the routine returns a NULL value when any of the input parameters are NULL. The routine is not invoked with a NULL input value. The CALLED ON NULL INPUT characteristic declares that the routine is invoked with NULL input parameter values. The RETURNS NULL ON NULL INPUT and CALLED ON NULL INPUT characteristics are mutually exclusive, with CALLED ON NULL INPUT as the default. The security declaration of SECURITY INVOKER or SECURITY DEFINER is only valid for catalog routines. It sets the mode for processing the routine with the permissions of the user who calls the routine (INVOKER) or the user who created the routine (DEFINER). The body of the routine can either be a simple single RETURN statement with an expression, or compound list of statements in a BEGIN block. Routines must contain a RETURN statement at the end of the top-level block, even if it’s unreachable.

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Examples

A simple catalog function: 
CREATE FUNCTION example.default.meaning_of_life()
  RETURNS BIGINT
  RETURN 42;
And used: 
SELECT example.default.meaning_of_life(); -- returns 42
Equivalent usage with an inline function: 
WITH FUNCTION meaning_of_life()
  RETURNS BIGINT
  RETURN 42
SELECT meaning_of_life();
Further examples of varying complexity that cover usage of the FUNCTION statement in combination with other statements are available in the SQL routines examples documentation.

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See also

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