Deterministic Functions

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.