MySQL: IF / THEN statements in stored procedures

Question

I'm writing a stored procedure that uses multiple IF / THEN statements that also need to execute multiple queries if they evaluate to true. Problem is, I can't seem to find any examples of the appropriate syntax. From the MySQL dev handbook, it seems like I could have multiple queries in the "statement_list," but so far I can't get it to work.

Here's what I'm trying to do:

SET agency = 
  COALESCE((SELECT org_agency_o_id 
            FROM orgs_agencies 
            WHERE org_agency_code = maj_agency_cat)
              ,(SELECT min(org_id) 
                FROM orgs     
                WHERE org_name LIKE CONCAT('U.S.',SUBSTRING(maj_agency_cat,5)))) 

IF agency IS NULL THEN 
  -- execute multiple queries   
  INSERT INTO orgs (org_name
                   ,org_name_length
                   ,org_type
                   ,org_sub_types) 
  VALUES (CONCAT('U.S. ',SUBSTRING(maj_agency_cat,5))
         ,LENGTH(CONCAT('U.S. ',SUBSTRING(maj_agency_cat,5)))
         ,'org','Org,GovernmentEntity,Federal,Agency');

SET agency = LAST_INSERT_ID();
END IF;

The error:

You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'IF agency IS NULL THEN INSERT INTO orgs (org_name,org_name_length,org_type,' at line 53

Any ideas? I know it has to be something simple, so I would greatly appreciate anybody's input.

Answer 1

You got a few issues as far as I can see:

1. As David pointed out, each and every statement needs to be terminated by a ;
2. If you do a SELECT, better make sure it can only select one value by doing a LIMIT 1; If you've got an aggregate function like min() then only one value can come out.
3. If you writing the procedure using the CREATE PROCEDURE ... syntax, don't forget to set DELIMITER $$ before the CREATE PROCEDURE ... END $$ body and a DELIMITER ; after.
4. If you have multiple statements inside your IF THEN ... END IF block, it's a good idea to put them inside a BEGIN ... END; block.
5. If you have a return value, like agency here, why not make it a FUNCTION name (arg1: INTEGER) RETURNS INTEGER instead of a PROCEDURE name (IN arg1 INTEGER, OUT agency INTEGER). The function is much more versatile.

DELIMITER $$

CREATE PROCEDURE name(arg1 INTEGER, arg2 INTEGER, ...)
BEGIN

  SELECT SET agency = 
    COALESCE((SELECT org_agency_o_id 
            FROM orgs_agencies 
            WHERE org_agency_code = maj_agency_cat) LIMIT 1,
    (SELECT min(org_id) FROM orgs     
    WHERE org_name LIKE CONCAT('U.S.',SUBSTRING(maj_agency_cat,5)))); 

  IF agency IS NULL THEN BEGIN
    -- execute multiple queries   
    INSERT INTO orgs (org_name
                     ,org_name_length
                     ,org_type
                     ,org_sub_types) 
    VALUES (CONCAT('U.S. ',SUBSTRING(maj_agency_cat,5))
           ,LENGTH(CONCAT('U.S. ',SUBSTRING(maj_agency_cat,5)))
           ,'org','Org,GovernmentEntity,Federal,Agency');

    SET agency = LAST_INSERT_ID();
  END; END IF;
END $$

DELIMITER ;

Answer 2

No semicolon after your first SET statement.