Re: NULL values in cardinality counts

[Ingo Strüwing]

Though the mentioned change was applied to MyISAM, I ask you to repeat the question in the "General" forum. Since I am neither an SQL expert nor an optimizer expert, and I'm not that long with MySQL, I can only guess that this change was made to adapt MyISAM to the behaviour of other storage engines and the SQL standard. As far as I know, the comparison between two NULL values gives a NULL result. This is neither true nor false, but needs to be interpreted as such by MySQL. I guess that it is interpreted as false.

Concerning database design, it is generally not a good idea to have a column with a large number of NULL values. It is better to make another table with the values of this column. See for example "Luke Wellington, Laura Thomson: MySQL Tutorial, Chapter 3 Database Design Crash Course".