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From:Alexey Polyakov Date:September 21 2005 6:27pm
Subject:Re: Bad MySQL performance with LEFT JOINS in combination with BIGINT(16)Keys
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Looks like you don't have index on `lad_id` field in second table.
So when you do the first query, mysql first does a full scan of 2nd
table, then does eqref lookup for 1st table, which is rather fast
operation. But when you do the left join, it scans first table and for
each value of id does a scan of second table, which is performance
killer.

--
Alexey Polyakov
Thread
Bad MySQL performance with LEFT JOINS in combination with BIGINT(16)KeysChristofer Dutz21 Sep
  • Re: Bad MySQL performance with LEFT JOINS in combination with BIGINT(16)KeysDevananda21 Sep
    • Re: Bad MySQL performance with LEFT JOINS in combination with BIGINT(16)KeysChristofer Dutz21 Sep
      • Re: Bad MySQL performance with LEFT JOINS in combination with BIGINT(16)KeysAlexey Polyakov21 Sep