Deterministic functions

The optional DETERMINISTIC clause indicates that the function is deterministic.Deterministic functions always return the same result for the same set of inputs.Non-deterministic functions can return different results for each invocation, even for the same set of inputs.If a function is specified as deterministic, then such a function might not be called again if it has already been called once with the given set of inputs, and instead takes the result from a metadata cache.

Note

Current versions of Firebird do not cache results of deterministic functions.

Specifying the DETERMINISTIC clause is comparable to a “promise” that the function will return the same thing for equal inputs.At the moment, a deterministic function is considered an invariant, and works like other invariants.That is, they are computed and cached at the current execution level of a given statement.

This is easily demonstrated with an example:

CREATE FUNCTION FN_T
RETURNS DOUBLE PRECISION DETERMINISTIC
AS
BEGIN
  RETURN rand();
END;

-- the function will be evaluated twice and will return 2 different values
SELECT fn_t() FROM rdb$database
UNION ALL
SELECT fn_t() FROM rdb$database;

-- the function will be evaluated once and will return 2 identical values
WITH t (n) AS (
  SELECT 1 FROM rdb$database
  UNION ALL
  SELECT 2 FROM rdb$database
)
SELECT n, fn_t() FROM t;

SQL Security

The SQL SECURITY clause specifies the security context for executing other routines or inserting into other tables.When SQL Security is not specified, the default value of the database is applied at runtime.

The SQL SECURITY clause can only be specified for PSQL functions, and is not valid for functions defined in a package.

See also SQL Security in chapter Security.

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Variable, Cursor and Subroutine Declarations

The optional declarations section, located at the start of the body of the function definition, defines variables (including cursors) and subroutines local to the function.Local variable declarations follow the same rules as parameters regarding specification of the data type.See details in the PSQL chapter for DECLARE VARIABLE, DECLARE CURSOR, DECLARE FUNCTION, and DECLARE PROCEDURE.

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:

Administrators
Users with the CREATE FUNCTION privilege

The user who created the stored function becomes its owner.

`CREATE FUNCTION` Examples

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);

Creating a deterministic stored function

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

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

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
```

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

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;

`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

`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

`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;

`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

Deterministic Functions

Deterministic functions

SQL Security

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Variable, Cursor and Subroutine Declarations

Function Body

External UDR Functions

Who Can Create a Function

CREATE FUNCTION Examples

ALTER FUNCTION

Who Can Alter a Function

Examples of ALTER FUNCTION

CREATE OR ALTER FUNCTION

Examples of CREATE OR ALTER FUNCTION

DROP FUNCTION

Who Can Drop a Function

Examples of DROP FUNCTION

RECREATE FUNCTION

Examples of RECREATE FUNCTION

`CREATE FUNCTION` Examples

`ALTER FUNCTION`

Examples of `ALTER FUNCTION`

`CREATE OR ALTER FUNCTION`

Examples of `CREATE OR ALTER FUNCTION`

`DROP FUNCTION`

Examples of `DROP FUNCTION`

`RECREATE FUNCTION`

Examples of `RECREATE FUNCTION`