sql - mysql query with OR optimization -

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can following query optimized? indexes can created?

select column_a    table_b    join table_a  table_b.id_b = table_a.id_a      or table_b.id_b = table_a.id_b;

your query should be:

select column_a    table_b    join table_a on table_b.id_b in (table_a.id_a, table_a.id_b)

if don't provide on criteria join, mysql accepts being cross join -- result cartesian product (that's bad, unless that's want). if knew table column_a came from, might suggest different approach query...

index following:

  • table_b.id_b
  • table_a.id_a
  • table_a.id_b

the 2 columns in table_a covering index, rather separate ones.


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