From: "Dawid Kuroczko" > > 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. > If your PRIMARY KEY would allow NULL values, it would not be possible > to address these rows with NULL values (*) and therefore it would not > be a real primary key, by definiton. It would be a unique key. That would be true for the entire key, but not for each part of the key... Regards, Jigal. -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/[EMAIL PROTECTED]
