I want to remove constraints from my table. My query is: ALTER TABLE `tbl_magazine_issue` DROP CONSTRAINT `FK_tbl_magazine_issue_mst_users` But I got an error: #1064 – 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 ‘constraint FK_tbl_magazine_issue_mst_users‘ at line 1 11 … Read more
I have a table whose primary key is referenced in several other tables as a foreign key. For example: CREATE TABLE `X` ( `X_id` int NOT NULL auto_increment, `name` varchar(255) NOT NULL, PRIMARY KEY (`X_id`) ) CREATE TABLE `Y` ( `Y_id` int(11) NOT NULL auto_increment, `name` varchar(255) NOT NULL, `X_id` int DEFAULT NULL, PRIMARY KEY … Read more
I have a table which has several ID columns to other tables. I want a foreign key to force integrity only if I put data in there. If I do an update at a later time to populate that column, then it should also check the constraint. (This is likely database server dependant, I’m using … Read more
A user has many uploads. I want to add a column to the uploads table that references the user. What should the migration look like? Here is what I have. I’m not sure if I should use (1) :user_id, :int or (2) :user, :references. I’m not even sure if (2) works. Just trying to do … Read more
So I’m trying to add Foreign Key constraints to my database as a project requirement and it worked the first time or two on different tables, but I have two tables on which I get an error when trying to add the Foreign Key Constraints. The error message that I get is: ERROR 1215 (HY000): … Read more
I’ve been wrestling with this for a while and can’t quite figure out what’s happening. I have a Card entity which contains Sides (usually 2) – and both Cards and Sides have a Stage. I’m using EF Codefirst migrations and the migrations are failing with this error: Introducing FOREIGN KEY constraint ‘FK_dbo.Sides_dbo.Cards_CardId’ on table ‘Sides’ … Read more
I am trying to forward engineer my new schema onto my database server, but I can’t figure out why I am getting this error. I’ve tried to search for the answer here, but everything I’ve found has said to either set the database engine to InnoDB or to make sure the keys I’m trying to … Read more
Can anyone explain how to implement one-to-one, one-to-many and many-to-many relationships while designing tables with some examples? 4 Answers 4
I want to add a Foreign Key to a table called “katalog”. ALTER TABLE katalog ADD CONSTRAINT `fk_katalog_sprache` FOREIGN KEY (`Sprache`) REFERENCES `Sprache` (`ID`) ON DELETE SET NULL ON UPDATE SET NULL; When I try to do this, I get this error message: Error Code: 1005. Can’t create table ‘mytable.#sql-7fb1_7d3a’ (errno: 150) Error in INNODB … Read more
Please clarify two things for me: Can a Foreign key be NULL? Can a Foreign key be duplicate? As fair as I know, NULL shouldn’t be used in foreign keys, but in some application of mine I’m able to input NULL in both Oracle and SQL Server, and I don’t know why. 12 Answers 12
