sql - Proper field orders for covering index - MySQL -

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is there standard order create covering index table in mysql? meaning if have query has clause, order , fields in select statement, in order have fields index create covering index?

a covering index takes list of columns in comma separated list. list traversed/reviewed starting @ left side. if left column not used, index not used. meaning, having column list like:

col_a, col_b, col_c

if query not contain reference col_a, won't used. if order changed to:

col_c, col_b, col_a

...then col_c needs referenced in query. continuing use second covering index column example, col_b or col_a don't have in in query evaluation moves column column, left right.

column references index use can in following clauses:

  • select
  • where
  • group by
  • having
  • order by

reference:


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