CREATE FUNCTION

Function

CREATE FUNCTION creates a function.

Precautions

• If the parameters or return values of a function have precision, the precision is not checked.
• When creating a function, you are advised to explicitly specify the schemas of tables in the function definition. Otherwise, the function may fail to be executed.
• current_schema and search_path specified by SET during function creation are invalid. search_path and current_schema before and after function execution should be the same.
• If a function has output parameters, the SELECT statement uses the default values of the output parameters when calling the function. When the CALL statement calls the function, it requires that the output parameters must be specified. When the CALL statement calls an overloaded PACKAGE function, it can use the default values of the output parameters. For details, see examples in CALL.
• Only the functions compatible with PostgreSQL or those with the PACKAGE attribute can be overloaded. After REPLACE is specified, a new function is created instead of replacing a function if the number of parameters, parameter type, or return value is different.
• You can use the SELECT statement to specify different parameters using identical functions, but cannot use the CALL statement to call identical functions without the PACKAGE attribute.
• When you create a function, you cannot insert other agg functions out of the avg function or other functions.
• By default, the permissions to execute new functions are granted to PUBLIC. For details, see GRANT. You can revoke the default execution permissions from PUBLIC and grant them to other users as needed. To avoid the time window during which new functions can be accessed by all users, create functions in transactions and set function execution permissions.
• When functions without parameters are called inside another function, you can omit brackets and call functions using their names directly.
• When functions with output parameters are called inside another function which is an assignment expression, you can omit the output parameters of the called functions.
• Oracle-compatible functions support viewing, exporting, and importing parameter comments.
• Oracle-compatible functions support viewing, exporting, and importing comments between IS/AS and plsql_body.
• When creating a function, if the return type is a cursor, it should be noted that the out parameter comes first and the in parameter comes second.

Syntax

• Syntax (compatible with PostgreSQL) for creating a customized function:

  CreateFunction ::= CREATE [ OR REPLACE  ] FUNCTION function_name
          ( [  { argname [ argmode  ] argtype [  { DEFAULT  | ':='  | =  } expression  ]}  [, ...]  ] )
          [ RETURNS rettype [ DETERMINISTIC  ] | RETURNS TABLE (  { column_name column_type  }  [, ...] )]
          LANGUAGE lang_name
          { [
              {IMMUTABLE  | STABLE  | VOLATILE}
              | {SHIPPABLE | NOT SHIPPABLE}
              | [ NOT  ] LEAKPROOF
              | WINDOW
              | {CALLED ON NULL INPUT | RETURNS NULL ON NULL INPUT | STRICT}
              | {[ EXTERNAL  ] SECURITY INVOKER  | [ EXTERNAL  ] SECURITY DEFINER | AU
      THID DEFINER  | AUTHID CURRENT_USER}
              | {FENCED | NOT FENCED}
              | {PACKAGE}
              | COST execution_cost
              | ROWS result_rows
              | SET configuration_parameter { {TO | =} value | FROM CURRENT }
              | COMMENT 'text' 
          ] } [...]
          {
              AS 'definition'
              | AS 'obj_file', 'link_symbol'
          }

• O syntax of creating a customized function:

  CreateFunction ::= CREATE [ OR REPLACE  ] FUNCTION function_name
            ( [  { argname [ argmode  ] argtype [  { DEFAULT | ':=' | =  } expression  ] }
          [, ...]  ] )
            RETURN rettype [ DETERMINISTIC  ]
           { [
                {IMMUTABLE  | STABLE  | VOLATILE }
                | {SHIPPABLE | NOT SHIPPABLE}
                | {PACKAGE}
                | [ NOT  ] LEAKPROOF
                | {CALLED ON NULL INPUT  | RETURNS NULL ON NULL INPUT  | STRICT }
                | {[ EXTERNAL  ] SECURITY INVOKER  | [ EXTERNAL  ] SECURITY DEFINER | 
        AUTHID DEFINER  | AUTHID CURRENT_USER}
                | COST execution_cost
                | ROWS result_rows
                | SET configuration_parameter { {TO | =} value | FROM CURRENT }
                | COMMENT 'text' 
             ] } [...]
             {
                IS | AS
             } plsql_body

Parameter Description

• function_name

  Specifies the name of the function to create (optionally schema-qualified).

  Value range: a string. It must comply with the identifier naming convention, and can contain a maximum of 63 characters. If the value contains more than 63 characters, the database truncates it and retains the first 63 characters as the function name.

• argname

  Specifies the parameter name of the function.

  Value range: a string. It must comply with the identifier naming convention, and can contain a maximum of 63 characters. If the value contains more than 63 characters, the database truncates it and retains the first 63 characters as the function parameter name.

• argmode

  Specifies the parameter mode of the function.

  Value range: IN, OUT, INOUT, and VARIADIC. The default value is IN. The parameters of OUT and INOUT cannot be used in the function definition of RETURNS TABLE.

  NOTE: VARIADIC specifies parameters of the array type.

• argtype

  Specifies the data type of a function parameter. %TYPE or %ROWTYPE can be used to indirectly reference a variable or table type. For details, see Variable Definition Statements.

• expression

  Specifies the default expression of a parameter.

• rettype

  Specifies the return data type.

  When there is OUT or INOUT parameter, the RETURNS clause can be omitted. If the clause exists, the result type of the clause must be the same as that of the output parameter. If there are multiple output parameters, the result type of the clause is RECORD. Otherwise, the result type of the clause is the same as that of a single output parameter.

  The SETOF modifier indicates that the function will return a set of items, rather than a single item.

  Same as argtype, %TYPE or %ROWTYPE can also be used to indirectly reference types.

• column_name

  Specifies the column name.

• column_type

  Specifies the column type.

• definition

  Specifies a string constant defining a function. Its meaning depends on the language. It can be an internal function name, a path pointing to a target file, a SQL query, or text in a procedural language.

• DETERMINISTIC

  Specifies an interface compatible with the SQL syntax. You are not advised to use it.

• LANGUAGE lang_name

  Specifies the name of the language that is used to implement the function. It can be SQL, internal, or the name of a customized process language. To ensure downward compatibility, the name can use single quotation marks. Contents in single quotation marks must be capitalized.

• WINDOW

  Indicates that this function is a window function. The WINDOW attribute cannot be changed when replacing an existing function definition.

  NOTICE: For a customized window function, the value of LANGUAGE can only be internal, and the referenced internal function must be a window function.

• IMMUTABLE

  Specifies that the function always returns the same result if the parameter values are the same.

• STABLE

  Specifies that the function cannot modify the database, and that within a single table scan it will consistently return the same result for the same parameter value, but its result varies by SQL statements.

• VOLATILE

  Specifies that the function value can change in a single table scan and no optimization is performed.

• SHIPPABLE|NOT SHIPPABLE

  Specifies whether the function can be pushed down for execution. This port is reserved and is not recommended.

• FENCED|NOT FENCED

  Specifies whether the user-defined C function is executed in fenced or not-fenced mode. This port is reserved and is not recommended.

• PACKAGE

  Specifies whether the function can be overloaded. PostgreSQL-style functions can be overloaded, and this parameter is designed for functions of other styles.

  • All PACKAGE and non-PACKAGE functions cannot be overloaded or replaced.
  • PACKAGE functions do not support parameters of the VARIADIC type.
  • The PACKAGE attribute of functions cannot be modified.

• LEAKPROOF

  Specifies that the function has no side effects. LEAKPROOF can be set only by the system administrator.

• CALLED ON NULL INPUT

  Declares that some parameters of the function can be invoked in normal mode if the parameter values are null. This parameter can be omitted.

• RETURNS NULL ON NULL INPUT

  STRICT

  Specifies that the function always returns null whenever any of its parameters is null. If this parameter is specified, the function is not executed when there are null parameters; instead a null result is returned automatically.

  RETURNS NULL ON NULL INPUT and STRICT have the same functions.

• EXTERNAL

  The keyword EXTERNAL is allowed for SQL conformance, but it is optional since, unlike in SQL, this feature applies to all functions not only external ones.

• SECURITY INVOKER

  AUTHID CURRENT_USER

  Specifies that the function will be executed with the permissions of the user who invokes it. This parameter can be omitted.

  SECURITY INVOKER and AUTHID CURRENT_USER have the same functions.

• SECURITY DEFINER

  AUTHID DEFINER

  Specifies that the function will be executed with the permissions of the user who created it.

  AUTHID DEFINER and SECURITY DEFINER have the same functions.

• COST execution_cost

  Estimates the execution cost of a function.

  The unit of execution_cost is cpu_operator_cost.

  Value range: a positive integer

• ROWS result_rows

  Estimates the number of rows returned by the function. This is only allowed when the function is declared to return a set.

  Value range: a positive number. The default value is 1000.

• COMMENT 'text'

  Comments a function.

• configuration_parameter

  • value

    Sets a specified database session parameter to a specified value. If the value is DEFAULT or RESET, the default setting is used in the new session. OFF closes the setting.

    Value range: a string

    • DEFAULT
    • OFF
    • RESET

    Specifies the default value.

  • from current

    Uses the value of configuration_parameter of the current session.

• plsql_body

  Specifies the PL/SQL stored procedure body.

  NOTICE: When a user is created in the function body, the plaintext password is recorded in the log. You are not advised to do it.

Examples

-- Define a function as SQL query.
MogDB=# CREATE FUNCTION func_add_sql(integer, integer) RETURNS integer
    AS 'select $1 + $2;'
    LANGUAGE SQL
    IMMUTABLE
    RETURNS NULL ON NULL INPUT;

-- Add an integer by parameter name using PL/pgSQL.
MogDB=# CREATE OR REPLACE FUNCTION func_increment_plsql(i integer) RETURNS integer AS $$
        BEGIN
                RETURN i + 1;
        END;
$$ LANGUAGE plpgsql;

-- Return the RECORD type.
MogDB=# CREATE OR REPLACE FUNCTION func_increment_sql(i int, out result_1 bigint, out result_2 bigint)
returns SETOF RECORD
as $$
begin
    result_1 = i + 1;
    result_2 = i * 10;
return next;
end;
$$language plpgsql;

-- Return a record containing multiple output parameters.
MogDB=# CREATE FUNCTION func_dup_sql(in int, out f1 int, out f2 text)
    AS $$ SELECT $1, CAST($1 AS text) || ' is text' $$
    LANGUAGE SQL;

MogDB=# SELECT * FROM func_dup_sql(42);

-- Compute the sum of two integers and returning the result (if the input is null, the returned result is null):
MogDB=# CREATE FUNCTION func_add_sql2(num1 integer, num2 integer) RETURN integer
AS
BEGIN PAC
RETURN num1 + num2;
END;
/
-- Alter the execution rule of function func_add_sql2 to IMMUTABLE (that is, the same result is returned if the parameter remains unchanged).
MogDB=# ALTER FUNCTION func_add_sql2(INTEGER, INTEGER) IMMUTABLE;

-- Rename the func_add_sql2 function as add_two_number:
MogDB=# ALTER FUNCTION func_add_sql2(INTEGER, INTEGER) RENAME TO add_two_number;

-- Change the owner of function add_two_number to omm.
MogDB=# ALTER FUNCTION omm(INTEGER, INTEGER) OWNER TO omm;

-- Delete the function.
MogDB=# DROP FUNCTION add_two_number;
MogDB=# DROP FUNCTION func_increment_sql;
MogDB=# DROP FUNCTION func_dup_sql;
MogDB=# DROP FUNCTION func_increment_plsql;
MogDB=# DROP FUNCTION func_add_sql;

-- Set parameters.
MogDB=# set behavior_compat_options='proc_outparam_override';
-- Create functions.
MogDB=# CREATE or replace FUNCTION func1(in a integer, out b integer)
RETURNS int
AS $$
DECLARE
    c int;
    BEGIN
        c := 1;
        b := a + c;
        return c;
    END; $$
LANGUAGE 'plpgsql' NOT FENCED;
-- Return return and output parameters at the same time.
MogDB=# declare
    result integer;
    a integer := 2;
    b integer := NULL;
begin
    result := func1(a => a, b => b);
    raise info 'b is: %', b;
    raise info 'result is: %', result;
end;
/
INFO:  b is: 3
INFO:  result is: 1
ANONYMOUS BLOCK EXECUTE
-- Left assignment expressions are not supported.
MogDB=# declare
    result integer;
    a integer := 2;
    b integer := NULL;
begin
    result := func1(a => a, b => b) + 1;
    raise info 'b is: %', b;
    raise info 'result is: %', result;
end;
/
ERROR:  when invoking function func1, maybe input something superfluous.
CONTEXT:  compilation of PL/pgSQL function "inline_code_block" near line 3
-- out/inout in a stored procedure cannot be set to a constant.
MogDB=# declare
    result integer;
    a integer := 2;
    b integer := NULL;
begin
    result := func1(a => a, b => 10);
    raise info 'b is: %', b;
    raise info 'result is: %', result;
end;
/
ERROR:  when invoking function func1, no destination for argments "b"
CONTEXT:  compilation of PL/pgSQL function "inline_code_block" near line 3

Helpful Links

ALTER FUNCTION，DROP FUNCTION