What is the difference between function and procedure in PL/SQL?

Question

What is the difference between function and procedure in PL/SQL ?

Answer 1

A function can be in-lined into a SQL statement, e.g.

select foo
      ,fn_bar (foo)
  from foobar

Which cannot be done with a stored procedure. The architecture of the query optimiser limits what can be done with functions in this context, requiring that they are pure (i.e. the same inputs always produce the same output). This restricts what can be done in the function, but allows it to be used in-line in the query if it is defined to be "pure".

Otherwise, a function (not necessarily deterministic) can return a variable or a result set. In the case of a function returning a result set, you can join it against some other selection in a query. However, you cannot use a non-deterministic function like this in a correlated subquery as the optimiser cannot predict what sort of result set will be returned (this is computationally intractable, like the halting problem).

Answer 2

Both stored procedures and functions are named blocks that reside in the database and can be executed as and when required.

The major differences are:

1. A stored procedure can optionally return values using out parameters, but can also be written in a manner without returning a value. But, a function must return a value.

2. A stored procedure cannot be used in a SELECT statement whereas a function can be used in a SELECT statement.

Practically speaking, I would go for a stored procedure for a specific group of requirements and a function for a common requirement that could be shared across multiple scenarios. For example: comparing between two strings, or trimming them or taking the last portion, if we have a function for that, we could globally use it for any application that we have.

Answer 3

A procedure does not have a return value, whereas a function has.

Example:

CREATE OR REPLACE PROCEDURE my_proc
   (p_name IN VARCHAR2 := 'John') as begin ... end

CREATE OR REPLACE FUNCTION my_func
   (p_name IN VARCHAR2 := 'John') return varchar2 as begin ... end

Notice how the function has a return clause between the parameter list and the "as" keyword. This means that it is expected to have the last statement inside the body of the function read something like:

return(my_varchar2_local_variable);

Where my_varchar2_local_variable is some varchar2 that should be returned by that function.

Answer 4

In dead simple way it makes this meaning.

Functions :

These subprograms return a single value; mainly used to compute and return a value.

Procedure :

These subprograms do not return a value directly; mainly used to perform an action.

Example Program:

CREATE OR REPLACE PROCEDURE greetings

BEGIN 

dbms_output.put_line('Hello World!');

END ;
/

Executing a Standalone Procedure :

A standalone procedure can be called in two ways:

• Using the EXECUTE keyword • Calling the name of procedure from a PL/SQL block

The procedure can also be called from another PL/SQL block:

BEGIN 
greetings;
END;
/

Function:

CREATE OR REPLACE FUNCTION totalEmployees 
RETURN number IS
total number(3) := 0;
BEGIN 
SELECT count(*) into total 
FROM employees;
RETURN total; 
END;
/

Following program calls the function totalCustomers from an another block

DECLARE 
c number(3);
BEGIN 
c := totalEmployees();
dbms_output.put_line('Total no. of Employees: ' || c);
END;
/

Answer 5

1. we can call a stored procedure inside stored Procedure,Function within function ,StoredProcedure within function but we can not call function within stored procedure.
2. we can call function inside select statement.
3. We can return value from function without passing output parameter as a parameter to the stored procedure.

This is what the difference i found. Please let me know if any .

Answer 6

In the few words - function returns something. You can use function in SQL query. Procedure is part of code to do something with data but you can not invoke procedure from query, you have to run it in PL/SQL block.