Am 19.03.2014 16:27, schrieb Morgan Tocker:
you can call me Harald
>>> The order of the WHERE clause does not matter
>> that is simply not true
>> otherwise that documentation would not exist
> Yes, the order of the columns in composite indexes *does matter*. This is a
> different question to what Christophe asked.
the question was "is there any performance impact"
and (DWProcessed / Lowest cardinality and indexed)
so *yes* it does matter, i have seen MySQL more than once not using any
index because a unlucky order of where clauses up to copy a 16 GB
table in a table file instead using a existing primary key
SELECT * FROM Status WHERE DWProcessed = 0 AND PreviousStatus NOT IN
('PENDING', 'ACCEPTED') AND SubscribeDate < DATE_SUB(NOW(), INTERVAL 24
I'd like the first filter (DWProcessed / Lowest cardinality and indexed)
Is there any performance impact on query processing, about the order of
WHERE clauses ?
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