Hi!
>>>>> "Philip" == Philip Lijnzaad <lijnzaad@stripped> writes:
Philip> On Thu, 15 Mar 2001 15:47:08 +0200 (EET),
Philip> "Michael" == Michael Widenius <monty@stripped> wrote:
Michael> Check the 'rows' column. According to this the 'weight' of the query
Michael> is about 8*1829*2920 = 42 M rows
Philip> <snip>
Michael> And the weight of this is just: 292016*19*8 = 44 M rows. Using disk
Michael> scanning this is reduced to 'just' 4M rows, as you can read about 10
Michael> rows while scanning at the same time you read one row with indexing.
Philip> Ah, that starts to make sense! Many many thanks. I am still a bit puzzled why
Philip> MySQL ignore my `USE INDEX(PRIMARY)' hint though.
It didn't.
The USE INDEX(PRIMARY) just tells MySQL that this is the only index it
should use. In this case it decided that a table scan was even better
than using this index.
Regards,
Monty
