mysql - The ordering of indexes group -

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i read somewhere there different between these 2 indexes groups:

  • add key id_user (id_user,seen);
  • add key id_user (seen,id_user);

well there? if yes order should based on parameter?

in reality have these 2 queries on 1 table:

query1:

select * mytable id_user = :id , seen null

query2:

select * mytable id_user = :id , timestamp > :tm

so kind of indexes proper in case? have 3 separated indexed on id_user, seen, timestamp columns.

both queries have equality condition on id_user. hence, either can take advantage of index id_user first key in index. so, recommend first index mention.

mysql has documentation on multi-column indexes. suggest start there learn them.

your query can take advantage of indexes on (id_user, seen) , (id_user, timestamp). probably, first key important. should try different indexes , see best meet performance goals.


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