>Create table events ( >uid BIGINT NOT NULL AUTO_INCREMENT, >name VARCHAR(255), >start_date DATE, >duration INTEGER, >location_id BIGINT, >primary key (uid) >); > >Create table locations ( >uid BIGINT NOT NULL AUTO_INCREMENT, >name VARCHAR(255), >address VARCHAR(255), >primary key (uid) >) > >Alter table events add index (location_id), add >Constraint FKB307E11920EBB9E5 foreign key (location_id) references >locations(uid) >// Here is my conclusion, and I was hoping someone may back this up. >Events has a primary key of UID that is auto_incremeneted. >Locations has a primary key of UID that is also incremented. > >The constraint and index are where I have questions. What is the index >and constraint doing? I can't seem to get my mind around what that alter >statement is trying to accomplish.
Well, the index part is adding, guess what, an index for column "location_id", and the constraint part is adding a referential constraint. That is, values in column events.location_id need to exist in table "locations.uid". The referential constraint is only enforced for InnoDB tables. Martijn Tonies Database Workbench - tool for InterBase, Firebird, MySQL, NexusDB, Oracle & MS SQL Server Upscene Productions http://www.upscene.com My thoughts: http://blog.upscene.com/martijn/ Database development questions? Check the forum! http://www.databasedevelopmentforum.com -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/[EMAIL PROTECTED]
