foreign-keys

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 Mysql has a special syntax for dropping foreign key constraints: ALTER TABLE tbl_magazine_issue DROP FOREIGN KEY FK_tbl_magazine_issue_mst_users I had the same problem and I got to solve with this code: ALTER TABLE `table_name` DROP FOREIGN

When you study relational theory foreign keys are, of course, mandatory. But in practice, in every place I worked, table products and joins are always done by specifying the keys explicitly in the query, instead of relying on foreign keys in the DBMS. This way, you could of course join two tables by fields that are not meant to be foreign keys, having unexpected results. Why do you think that is? Shouldn't DBMSs enforce that Joins and Products be made only by foreign keys? EDIT: Thanks for all the answers. It's clear to me now that the main reason for FKs is reference integrity. But if you

If I want to delete all the tables in my database like this, will it take care of the foreign key constraint? If not, how do I take care of that first? GO IF OBJECT_ID('dbo.[Course]','U') IS NOT NULL DROP TABLE dbo.[Course] GO IF OBJECT_ID('dbo.[Student]','U') IS NOT NULL DROP TABLE dbo.[Student] marc_s No, this will not drop your table if there are indeed foreign keys referencing it. To get all foreign key relationships referencing your table, you could use this SQL (if you're on SQL Server 2005 and up): SELECT * FROM sys.foreign_keys WHERE referenced_object_id = object_id('Student') and if

When I try to create these two tables I get: "SQL Error: ORA-00904: "COLLECTIBLENUM": invalid identifier" I'm sure it's a noob error but I'm just not seeing it. Can someone please point out what I'm doing wrong? Thanks in advance. CREATE TABLE Collectibles( CollectibleNum Number(10) NOT NULL, CONSTRAINT collectibles_pk PRIMARY KEY(CollectibleNum)); Create table DiecastItems( DiecastName VARCHAR2(45) NOT NULL, DiecastCopy NUMBER(2) NOT NULL, DiecastScale VARCHAR2(25), ColorScheme VARCHAR2(25), DiecastYear NUMBER(4), CONSTRAINT diecastItem_pk PRIMARY KEY(DiecastName, DiecastCopy), CONSTRAINT

In MSSQL 2005 I just struck the infamous error message: Introducing FOREIGN KEY constraint XXX on table YYY may cause cycles or multiple cascade paths. Specify ON DELETE NO ACTION or ON UPDATE NO ACTION, or modify other FOREIGN KEY constraints. Now, StackOverflow has several topics about this error message, so I've already got the solution (in my case I'll have to use triggers), but I'm curious as to why there is such a problem at all. As I understand it, there are basically two scenarios that they want to avoid - a cycle and multiple paths. A cycle would be where two tables have cascading

I am trying to figure out how to structure this database. I have used Apple's core data before just fine, I'm just working on a different project now that requires MySQL. I am very new to MySQL so please go easy on me. :) For this example, let's say I have three tables, User , Device , and Location . Drawing it out, a Location can have many Device s, but the Device can only have one Location ; Each User has its primary key, UserID , of which I need to use to fetch the correct information. So how do I create a relationship like this here? I've heard of creating an index and a foreign key and I