check if column exists before ALTER TABLE — mysql


Is there a way to check if a column exists in a mySQL DB prior to (or as) the ALTER TABLE ADD coumn_name statement runs? Sort of an IF column DOES NOT EXIST ALTER TABLE thing.

I've tried ALTER IGNORE TABLE my_table ADD my_column but this still throws the error if the column I'm adding already exists.

EDIT: use case is to upgrade a table in an already installed web app-- so to keep things simple, I want to make sure the columns I need exist, and if they don't, add them using ALTER TABLE


Answers:


Since mysql control statements (e.g. "IF") only work in stored procedures, a temporary one can be created and executed:

DROP PROCEDURE IF EXISTS add_version_to_actor;

DELIMITER $$

CREATE DEFINER=CURRENT_USER PROCEDURE add_version_to_actor ( ) 
BEGIN
DECLARE colName TEXT;
SELECT column_name INTO colName
FROM information_schema.columns 
WHERE table_schema = 'connjur'
    AND table_name = 'actor'
AND column_name = 'version';

IF colName is null THEN 
    ALTER TABLE  actor ADD  version TINYINT NOT NULL DEFAULT  '1' COMMENT  'code version of actor when stored';
END IF; 
END$$

DELIMITER ;

CALL add_version_to_actor;

DROP PROCEDURE add_version_to_actor;