If those were your real queries, I'd say a table scan is appropriate, as you are asking for every row (no WHERE condition, just a join).
This would be a lot easier to answer if you'd actually show us the EXPLAIN output.
Michael
Nick Arnett wrote:
I'm updating one table with data from another and finding that the server is doing a table scan on the second table, even though it's a simple join on the primary keys. This doesn't seem right. The query looks liket this:
UPDATE a SET a.y TO b.a WHERE a.primary_key = b.primary_key
and if I do the equivalent SELECT:
EXPLAIN SELECT * FROM a, b WHERE a.primary_key = b.primary_key
it shows that it's doing a table scan on table b.
Is this normal? Is it because primary keys are unique? I had imagined that this would be a very fast operation, but it's not, it's surprisingly slow.
Nick
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