Using 5.0.67-0ubuntu6 on Ubuntu 8.10.
I'm going through the "High Performance MySQL" book. I was reading
section 4.4.1.8, titled "MIN() and MAX()". The point of this is that
MySQL doesn't optimize MIN()/MAX() very well, but it showed a supposed
workaround for this.
The first sample query was:
SELECT MIN(actor_id) FROM sakila.actor WHERE first_name = 'PENELOPE';
As described, this does a table scan, looking at 200 rows.
The alternative was this:
SELECT actor_id FROM sakila.actor USE INDEX(PRIMARY) WHERE
first_name = 'PENELOPE' LIMIT 1;
Which supposedly would not do a full table scan, and it seems logical.
The explain output for this is the following (tabs replaced with colon):
id:select_type:table:type:possible_keys:key:key_len:ref:rows:Extra
1:SIMPLE:actor:ALL:<null>:<null>:<null>:<null>:200:Using where
This explain output is identical to the output for the previous query,
so this workaround didn't appear to help any.
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