How to remove constraints from my MySQL table?
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 … Read more
foreign-keys
How to find all tables that have foreign keys that reference particular table.column and have values for those foreign keys?
I have a table whose primary key is referenced in several other tables as a foreign key. For example: CREATE TABLE `X` ( … Read more
Can table columns with a Foreign Key be NULL?
I have a table which has several ID columns to other tables. I want a foreign key to force integrity only if I … Read more
Add a reference column migration in Rails 4
A user has many uploads. I want to add a column to the uploads table that references the user. What should the migration … Read more
MySQL Cannot Add Foreign Key Constraint
So I’m trying to add Foreign Key constraints to my database as a project requirement and it worked the first time or two … Read more
Introducing FOREIGN KEY constraint may cause cycles or multiple cascade paths – why?
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 … Read more
MySQL Error 1215: Cannot add foreign key constraint
I am trying to forward engineer my new schema onto my database server, but I can’t figure out why I am getting this … Read more
How to implement one-to-one, one-to-many and many-to-many relationships while designing tables?
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
Add Foreign Key to existing table
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` … Read more
Can a foreign key be NULL and/or duplicate?
Please clarify two things for me: Can a Foreign key be NULL? Can a Foreign key be duplicate? As fair as I know, … Read more