Mysql - How to quit/exit from stored procedure

Question

CREATE PROCEDURE SP_Reporting(IN tablename VARCHAR(20))
proc_label:BEGIN
     IF tablename IS NULL THEN
          LEAVE proc_label;
     END IF;

     #proceed the code
END;

If you want an "early exit" for a situation in which there was no error, then use the accepted answer posted by @piotrm. Most typically, however, you will be bailing due to an error condition (especially in a SQL procedure).

As of MySQL v5.5 you can throw an exception. Negating exception handlers, etc. that will achieve the same result, but in a cleaner, more precise manner.

Here's how:

DECLARE CUSTOM_EXCEPTION CONDITION FOR SQLSTATE '45000';

IF <Some Error Condition> THEN      
    SIGNAL CUSTOM_EXCEPTION
    SET MESSAGE_TEXT = 'Your Custom Error Message';
END IF;     

Note SQLSTATE '45000' equates to "Unhandled user-defined exception condition". By default, this will produce an error code of 1644 (which has that same meaning). Note that you can throw other condition codes or error codes if you want (plus additional details for exception handling).

For more on this subject, check out:

https://dev.mysql.com/doc/refman/5.5/en/signal.html

How to raise an error within a MySQL function

http://www.databasejournal.com/features/mysql/mysql-error-handling-using-the-signal-and-resignal-statements.html

Addendum

As I'm re-reading this post of mine, I realized I had something additional to add. Prior to MySQL v5.5, there was a way to emulate throwing an exception. It's not the same thing exactly, but this was the analogue: Create an error via calling a procedure which does not exist. Call the procedure by a name which is meaningful in order to get a useful means by which to determine what the problem was. When the error occurs, you'll get to see the line of failure (depending on your execution context).

For example:

CALL AttemptedToInsertSomethingInvalid;

Note that when you create a procedure, there is no validation performed on such things. So while in something like a compiled language, you could never call a function that wasn't there, in a script like this it will simply fail at runtime, which is exactly what is desired in this case!

To handle this situation in a portable way (ie will work on all databases because it doesn’t use MySQL label Kung fu), break the procedure up into logic parts, like this:

CREATE PROCEDURE SP_Reporting(IN tablename VARCHAR(20))
BEGIN
     IF tablename IS NOT NULL THEN
         CALL SP_Reporting_2(tablename);
     END IF;
END;

CREATE PROCEDURE SP_Reporting_2(IN tablename VARCHAR(20))
BEGIN
     #proceed with code
END;

This works for me :

 CREATE DEFINER=`root`@`%` PROCEDURE `save_package_as_template`( IN package_id int , 
IN bus_fun_temp_id int  , OUT o_message VARCHAR (50) ,
            OUT o_number INT )
 BEGIN

DECLARE  v_pkg_name  varchar(50) ;

DECLARE  v_pkg_temp_id  int(10)  ; 

DECLARE  v_workflow_count INT(10);

-- checking if workflow created for package
select count(*)  INTO v_workflow_count from workflow w where w.package_id = 
package_id ;

this_proc:BEGIN   -- this_proc block start here 

 IF  v_workflow_count = 0 THEN
   select 'no work flow ' as 'workflow_status' ;
    SET o_message ='Work flow is not created for this package.';
    SET  o_number = -2 ;
      LEAVE this_proc;
 END IF;

select 'work flow  created ' as 'workflow_status' ;
-- To  send some message
SET o_message ='SUCCESSFUL';
SET  o_number = 1 ;

  END ;-- this_proc block end here 

END

Why not this:

CREATE PROCEDURE SP_Reporting(IN tablename VARCHAR(20))
BEGIN
     IF tablename IS NOT NULL THEN
          #proceed the code
     END IF;
     # Do nothing otherwise
END;