Drop foreign key only if it exists

Question

I\'m on a MySQL database.

I\'m doing this, but it doesn\'t work.

ALTER TABLE `object` DROP FOREIGN KEY IF EXISTS `object_ibfk_1`;

I\'ve

Answer 1

For greater re-usability, you would indeed want to use a stored procedure. Run this code once on your desired DB:

   DROP PROCEDURE IF EXISTS PROC_DROP_FOREIGN_KEY;
    DELIMITER $$
    CREATE PROCEDURE PROC_DROP_FOREIGN_KEY(IN tableName VARCHAR(64), IN constraintName VARCHAR(64))
    BEGIN
        IF EXISTS(
            SELECT * FROM information_schema.table_constraints
            WHERE 
                table_schema    = DATABASE()     AND
                table_name      = tableName      AND
                constraint_name = constraintName AND
                constraint_type = 'FOREIGN KEY')
        THEN
            SET @query = CONCAT('ALTER TABLE ', tableName, ' DROP FOREIGN KEY ', constraintName, ';');
            PREPARE stmt FROM @query; 
            EXECUTE stmt; 
            DEALLOCATE PREPARE stmt; 
        END IF; 
    END$$
    DELIMITER ;

Thereafter, you can always replace this:

ALTER TABLE `object` DROP FOREIGN KEY IF EXISTS `object_ibfk_1`;

with this:

CALL PROC_DROP_FOREIGN_KEY('object', 'object_ibfk_1');

Your script should then run smoothly whether object_ibfk_1 actually exists or not.

A lot of credit due to: http://simpcode.blogspot.com.ng/2015/03/mysql-drop-foreign-key-if-exists.html