mysql - Query takes too long to run -


i running below query retrive unique latest result based on date field within same table. query takes time when table growing. suggestion improve welcome.

select     t2.*     (         select             (                 select                     id                                     ctc_pre_assets ti                                     ti.ctcassettag = t1.ctcassettag                 order                     ti.createddate desc limit 1             ) lid                     (                 select                     distinct ctcassettag                                     ctc_pre_assets             ) t1     ) ro,     ctc_pre_assets t2     t2.id = ro.lid order     id

our able may contain same row multiple times, each row different time stamp. object based on single column example assettag want retrieve single row each assettag latest timestamp.

it's simpler, , faster, find newest date each ctcassettag , join find whole row matches.

this assume no ctcassettag has multiple rows same createddate, in case can more 1 row per ctcassettag.

select     ctc_pre_assets.*     ctc_pre_assets inner join (     select         ctcassettag,         max(createddate)   createddate             ctc_pre_assets     group         ctcassettag )    newest        on  newest.ctcassettag = ctc_pre_assets.ctcassettag        , newest.createddate = ctc_pre_assets.createddate order     ctc_pre_assets.id

edit: deal multiple rows same date.

you haven't said how pick row want in event multiple rows same ctcassettag on same createddate. so, solution chooses row lowest id amongst duplicates.

select     ctc_pre_assets.*     ctc_pre_assets     ctc_pre_assets.id     =     (         select             lookup.id                     ctc_pre_assets   lookup                     lookup.ctcassettag = ctc_pre_assets.ctcassettag         order             lookup.createddate  desc,             lookup.id           asc         limit             1     )

this still use correlated sub-query, slower simple nested-sub-query (such first answer), deal "duplicates".

you can change rules on row pick changing order by in correlated sub-query.

it's similar own query, 1 less join.


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