Re: why must i specify an index in query?
Peter, I think I'll use that query because long-term that will be the best option due to speed and data volume.
I understand MySQL didn't use the index on the first query, because it's cardinality was only 2. If an index with cardinality can speed a query up 15 fold (perhaps 1000x fold if the data volume were larger), it's obviously an enormous impact.
I am still interested in understanding why MySQL would ever not use an index; what's the advantage of not using one? I can't think of why MySQL would ever opt to not use an index, but there's obviously some reasoning.
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Re: why must i specify an index in query?
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