Does MySQL index NULL values?

Question

I have a MySQL table where an indexed INT column is going to be 0 for 90% of the rows. If I change those rows to use NULL instead of 0, will they b

Answer 1

Allowing a column to be null will add a byte to the storage requirements of the column. This will lead to an increased index size which is probably not good. That said if a lot of your queries are changed to use "IS NULL" or "NOT NULL" they might be overall faster than doing value comparisons.

My gut would tell me not null, but there's one answer: test!