Next point is that MySQL will only make use of an index in a join or a
where clause if ONLY that field is included in the index. If you pack 3
fields into an index and then try to join on ONLY ONE field, the index
can't be used. So look at your joins and where clauses and make sure
your indexes match.
I think that you can use the left most columns of the index, without including the
So a join on
MSIISDN and ACTIV_IMEI
may use the index (depending on whatever else is going on)
but a join on ACTIV_IMEI only or MSISDN and ACTIV_TIME won't.
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