> > > It can't have anything to do with the 'uniqueness' of the data, since I > can > > > have a lot of 'zero'-values in the column, as long as the combination of > > > columns in the PRIMARY key results in unique values. > > > > Because it is a PRIMARY KEY. I mean phrase 'PRIMARY KEY' means "a key > > with which each row can be explicitly addressed". So if you have 2000 > > rows in a table, you can write 2000 SELECT statemens which will use > > columns in primary key and each of these SELECT statements will > > return exactly one (different) row. > With the NULL values included it will still uniquely identify each row... > > I would understand it if it would mean that the key as a whole could not be > NULL, but the restriction that each column that is part of a PRIMARY KEY > must have the NOT NULL constraint is not logical.
It isn't? Imagine this: mytable with PK (id, value) 1, NULL 1, NULL 2, value 2, NULL now, given that NULL <> NULL ... what row would 1, NULL identify? Or would you only allow a single NULL for each part of the PK? With regards, Martijn Tonies Database Workbench - developer tool for InterBase, Firebird, MySQL & MS SQL Server Upscene Productions http://www.upscene.com -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/[EMAIL PROTECTED]
