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 PROCEDUREEXTERNAL FUNCTION 

Function Body

The header section is followed by the function body, consisting of one or more PSQL statements enclosed between the outer keywords BEGIN and END.Multiple BEGIN …​ END blocks of terminated statements may be embedded inside the procedure body.

External UDR Functions

A stored function can also be located in an external module.In this case, instead of a function body, the CREATE FUNCTION specifies the location of the function in the external module using the EXTERNAL clause.The optional NAME clause specifies the name of the external module, the name of the function inside the module, and — optionally — user-defined information.The required ENGINE clause specifies the name of the UDR engine that handles communication between Firebird and the external module.The optional AS clause accepts a string literal “body”, which can be used by the engine or module for various purposes.

Warning

External UDR (User Defined Routine) functions created using CREATE FUNCTION …​ EXTERNAL …​ should not be confused with legacy UDFs (User Defined Functions) declared using DECLARE EXTERNAL FUNCTION.

UDFs are deprecated, and a legacy from previous Firebird functions.Their capabilities are significantly inferior to the capabilities to the new type of external UDR functions.

Who Can Create a Function

The CREATE FUNCTION statement can be executed by:

The user who created the stored function becomes its owner.

CREATE FUNCTION Examples

  1. Creating a stored function

    CREATE FUNCTION ADD_INT (A INT, B INT DEFAULT 0)
RETURNS INT
AS
BEGIN
  RETURN A + B;
END

    Calling in a select:

    SELECT ADD_INT(2, 3) AS R FROM RDB$DATABASE

    Call inside PSQL code, the second optional parameter is not specified:

    MY_VAR = ADD_INT(A);

  2. Creating a deterministic stored function

    CREATE FUNCTION FN_E()
RETURNS DOUBLE PRECISION DETERMINISTIC
AS
BEGIN
  RETURN EXP(1);
END

  3. Creating a stored function with table column type parameters

    Returns the name of a type by field name and value

    CREATE FUNCTION GET_MNEMONIC (
  AFIELD_NAME TYPE OF COLUMN RDB$TYPES.RDB$FIELD_NAME,
  ATYPE TYPE OF COLUMN RDB$TYPES.RDB$TYPE)
RETURNS TYPE OF COLUMN RDB$TYPES.RDB$TYPE_NAME
AS
BEGIN
  RETURN (SELECT RDB$TYPE_NAME
          FROM RDB$TYPES
          WHERE RDB$FIELD_NAME = :AFIELD_NAME
          AND RDB$TYPE = :ATYPE);
END

  4. Creating an external stored function

    Create a function located in an external module (UDR).Function implementation is located in the external module udrcpp_example.The name of the function inside the module is wait_event.

    CREATE FUNCTION wait_event (
  event_name varchar (31) CHARACTER SET ascii
) RETURNS INTEGER
EXTERNAL NAME 'udrcpp_example!Wait_event'
ENGINE udr

  5. Creating a stored function containing a sub-function

    Creating a function to convert a number to hexadecimal format.

    CREATE FUNCTION INT_TO_HEX (
  ANumber BIGINT ,
  AByte_Per_Number SMALLINT = 8)
RETURNS CHAR (66)
AS
DECLARE VARIABLE xMod SMALLINT ;
DECLARE VARIABLE xResult VARCHAR (64);
DECLARE FUNCTION TO_HEX (ANum SMALLINT ) RETURNS CHAR
  AS
  BEGIN
    RETURN CASE ANum
      WHEN 0 THEN '0'
      WHEN 1 THEN '1'
      WHEN 2 THEN '2'
      WHEN 3 THEN '3'
      WHEN 4 THEN '4'
      WHEN 5 THEN '5'
      WHEN 6 THEN '6'
      WHEN 7 THEN '7'
      WHEN 8 THEN '8'
      WHEN 9 THEN '9'
      WHEN 10 THEN 'A'
      WHEN 11 THEN 'B'
      WHEN 12 THEN 'C'
      WHEN 13 THEN 'D'
      WHEN 14 THEN 'E'
      WHEN 15 THEN 'F'
      ELSE NULL
    END;
  END
BEGIN
  xMod = MOD (ANumber, 16);
  ANumber = ANumber / 16;
  xResult = TO_HEX (xMod);
  WHILE (ANUMBER> 0) DO
  BEGIN
    xMod = MOD (ANumber, 16);
    ANumber = ANumber / 16;
    xResult = TO_HEX (xMod) || xResult;
  END
  RETURN '0x' || LPAD (xResult, AByte_Per_Number * 2, '0' );
END

  6. With DEFINER set for function f, user US needs only the EXECUTE privilege on f.If it were set for INVOKER, the user would also need the INSERT privilege on table t.

    set term ^;
create function f (i integer) returns int SQL SECURITY DEFINER
as
begin
  insert into t values (:i);
  return i + 1;
end^
set term ;^
grant execute on function f to user us;

commit;

connect 'localhost:/tmp/59.fdb' user us password 'pas';
select f(3) from rdb$database;
See also

[fblangref50-ddl-func-creatalter], [fblangref50-ddl-func-alter], [fblangref50-ddl-func-recreate], [fblangref50-ddl-func-drop], [fblangref50-ddl-extfunc-declare]

ALTER FUNCTION

Alters a stored function

Available in

DSQL

Syntax
ALTER FUNCTION funcname
  [ ( [ <in_params> ] ) ]
  RETURNS <domain_or_non_array_type> [COLLATE collation]
  [DETERMINISTIC]
  {<psql_function> | <external-module-body>}

!! See syntax of CREATE FUNCTION for further rules !!

The ALTER FUNCTION statement allows the following changes to a stored function definition:

  • the set and characteristics of input and output type

  • local variables, named cursors, and subroutines

  • code in the body of the stored procedure

For external functions (UDR), you can change the entry point and engine name.For legacy external functions declared using DECLARE EXTERNAL FUNCTION — also known as UDFs — it is not possible to convert to PSQL and vice versa.

After ALTER FUNCTION executes, existing privileges remain intact and dependencies are not affected.

Altering a function without specifying the SQL SECURITY clause will remove the SQL Security property if currently set for this function.This means the behaviour will revert to the database default.

Caution

Take care about changing the number and type of input parameters and the output type of a stored function.Existing application code and procedures, functions and triggers that call it could become invalid because the new description of the parameters is incompatible with the old calling format.For information on how to troubleshoot such a situation, see the article The RDB$VALID_BLR Field in the Appendix.

Who Can Alter a Function

The ALTER FUNCTION statement can be executed by:

  • Administrators

  • Owner of the stored function

  • Users with the ALTER ANY FUNCTION privilege

Examples of ALTER FUNCTION

Altering a stored function
ALTER FUNCTION ADD_INT(A INT, B INT, C INT)
RETURNS INT
AS
BEGIN
  RETURN A + B + C;
END
See also

[fblangref50-ddl-func-create], [fblangref50-ddl-func-creatalter], [fblangref50-ddl-func-recreate], [fblangref50-ddl-func-drop]

CREATE OR ALTER FUNCTION

Creates a stored function if it does not exist, or alters a stored function

Available in

DSQL

Syntax
CREATE OR ALTER FUNCTION funcname
  [ ( [ <in_params> ] ) ]
  RETURNS <domain_or_non_array_type> [COLLATE collation]
  [DETERMINISTIC]
  {<psql_function> | <external-module-body>}

!! See syntax of CREATE FUNCTION for further rules !!

The CREATE OR ALTER FUNCTION statement creates a new stored function or alters an existing one.If the stored function does not exist, it will be created by invoking a CREATE FUNCTION statement transparently.If the function already exists, it will be altered and compiled (through ALTER FUNCTION) without affecting its existing privileges and dependencies.

Examples of CREATE OR ALTER FUNCTION

Create a new or alter an existing stored function
CREATE OR ALTER FUNCTION ADD_INT(A INT, B INT DEFAULT 0)
RETURNS INT
AS
BEGIN
  RETURN A + B;
END
See also

[fblangref50-ddl-func-create], [fblangref50-ddl-func-alter], [fblangref50-ddl-func-drop]

DROP FUNCTION

Drops a stored function

Available in

DSQL

Syntax
DROP FUNCTION funcname
Table 1. DROP FUNCTION Statement Parameters
Parameter Description

funcname

Stored function name.The maximum length is 63 characters.Must be unique among all function names in the database.

The DROP FUNCTION statement deletes an existing stored function.If the stored function has any dependencies, the attempt to delete it will fail, and raise an error.

Who Can Drop a Function

The DROP FUNCTION statement can be executed by:

  • Administrators

  • Owner of the stored function

  • Users with the DROP ANY FUNCTION privilege

Examples of DROP FUNCTION

DROP FUNCTION ADD_INT;
See also

[fblangref50-ddl-func-create], [fblangref50-ddl-func-creatalter], [fblangref50-ddl-func-recreate]

RECREATE FUNCTION

Drops a stored function if it exists, and creates a stored function

Available in

DSQL

Syntax
RECREATE FUNCTION funcname
  [ ( [ <in_params> ] ) ]
  RETURNS <domain_or_non_array_type> [COLLATE collation]
  [DETERMINISTIC]
  {<psql_function> | <external-module-body>}

!! See syntax of CREATE FUNCTION for further rules !!

The RECREATE FUNCTION statement creates a new stored function or recreates an existing one.If there is a function with this name already, the engine will try to drop it and then create a new one.Recreating an existing function will fail at COMMIT if the function has dependencies.

Note

Be aware that dependency errors are not detected until the COMMIT phase of this operation.

After a procedure is successfully recreated, existing privileges to execute the stored function and theprivileges of the stored function itself are dropped.

Examples of RECREATE FUNCTION

Creating or recreating a stored function
RECREATE FUNCTION ADD_INT(A INT, B INT DEFAULT 0)
RETURNS INT
AS
BEGIN
  RETURN A + B;
EN
See also

[fblangref50-ddl-func-create], [fblangref50-ddl-func-drop]