Functions
The function is a subprogram that calculates a value. The Functions and procedures are structured similar, except that the functions have a RETURN clause. You can write functions using the syntax as shown below:
FUNCTION name [(parameter[, parameter, ...])] RETURN datatype IS
[local declarations]
BEGIN
executable statements
[EXCEPTION
exception handlers]
END [name];
Where the parameter stand for the following syntax which is as shown below:
parameter_name [IN | OUT [NOCOPY] | IN OUT [NOCOPY]] datatype_name
[{:= | DEFAULT} expression]
The datatype of a parameter or function result cannot be constrained. Though, you can use a workaround to size-constrain them indirectly.
Similar to a procedure, a function has 2 parts: the specifications & the body. The function specification starts with the keyword FUNCTION and ends with the RETURN clause that specifies the datatype of the result value. The Parameter declarations are not obligatory.
The Functions that take no parameters are written without the parentheses. The function body starts with the keyword IS and ends with the keyword END followed by an optional function name. The function body has 3 parts: a declarative section, an executable section, & an optional exception-handling section.
The declarative section contains the local declarations, that are placed between the keywords IS & BEGIN. The keywords DECLARE is never used. The executable section contains statements that are placed between the keywords BEGIN and EXCEPTION (or END). One or more RETURN statements should appear in the executable section of a function. The exception-handling section contains exception handlers that are placed between the keywords EXCEPTION and END. Consider the function sal_ok, that determines if an employee salary is out of range:
FUNCTION sal_ok (salary REAL, title REAL) RETURN BOOLEAN IS
min_sal REAL;
max_sal REAL;
BEGIN
SELECT losal, hisal INTO min_sal, max_sal
FROM sals
WHERE job = title;
RETURN (salary >= min_sal) AND (salary <= max_sal);
END sal_ok;
Whenever called, this function accepts an employee salary and the job title. It uses the job title to select the range limits from the sals database table. The sal_ok, function identifier, is set to a Boolean value by the RETURN statement. When the salary is out of range, the sal_ok is set to FALSE; or else, the sal_ok is set to TRUE.
The function is called as the part of an expression. For illustration, the function sal_ok might be called as shown:
DECLARE
new_sal REAL;
new_title VARCHAR2(15);
BEGIN
...
IF sal_ok(new_sal, new_title) THEN ...
The function identifier sal_ok acts such as a variable whose value depends on the parameters passed to it.