Re: MIN on an indexed field too slow

[Björn Steinbrink]

Sorting and MIN()/MAX() only works on the suffix on an index and filtering (WHERE foo = 123) only works on a prefix of an index. In your case, the query is exactly the opposite, regarding the existing key.

If possible (I don't know what else you do with that table), you could just switch the order of the parts of your primary key. Otherwise, add an extra index on (recordType, recordNumber). That should make the MIN() value be found instantly.

Edit: If you can't switch the order of the primary key parts and don't need instant but just faster results, an index on recordNumber alone should already speed up the query a lot, as MySQL can then use the index to access the rows in ascending order and stop on the first match for recordType.