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Currently I’m running these two queries:
SELECT COUNT(*) FROM `mytable`
SELECT * FROM `mytable` WHERE `id`=123
I’m wondering what format will be the most efficient. Does the order the queries are executed make a difference? Is there a single query that will do what I want?
Both queries are fairly unrelated. The COUNT doesn’t use any indexes, while the SELECT likely uses the primary key for a fast look-up. The only thing the queries have in common is the table.
Since these are so simple, the query optimizer and results cache shouldn’t have a problem performing very well on these queries.
Are they causing you performance problems? If not, don’t bother optimizing them.