Originally Posted by shaunthomson
Can you use three columns that are unique together as the primary key, or is that not workable?
Didn't we have this discussion already.
Didn't we talk about "skipping" fields in multi-field indexes?
Didn't I even suggest that a good primary key would be
CREATE TABLE djBooks (
PRIMARY KEY( djid, booknum, songid )
And didn't I note the reasons for putting the fields in that order in the (yes, three field) primary key?
I even gave the examples:
-- a WHERE involving just DJID will use the index
-- a WHERE involving DJID and BOOKNUM will use the index
-- a WHERE involving all three fields will use the index
-- a WHERE involving just BOOKNUM will *NOT* use the index
-- a WHERE involving just SONGID will *NOT* use the index
-- a WHERE involving just BOOKNUM and SONGID will *NOT* use the index
-- a WHERE invovling just DJID and SONGID will use the index only for the DJID.
(All the above may not be true in other databases--SQL Server in particular--but it is a well document limitation of MySQL.)