sql - MySQL select rows with timestamp closest to but not exceeding the given timestamp -


i have table looks below

state_history +---------------------+-----------+----------------+      + | state_added_time    | entity_id | state_id       | .... | +---------------------+-----------+----------------+      | | 2015-05-15 13:24:22 |         1 |              1 |      | | 2015-05-15 13:29:44 |         3 |              2 |      | | 2015-05-15 13:34:26 |         2 |              2 |      | | 2015-05-15 14:24:28 |         1 |              3 |      | | 2015-05-15 14:24:30 |         2 |              3 |      | | 2015-05-15 14:26:32 |         3 |              5 |      | | 2015-05-15 14:26:34 |         3 |              3 |      | .......

my intention know states of entities @ given time. example, if timestamp received application 2015-05-15 14:25:00 expected output should be:

state_history +---------------------+-----------+----------------+      + | state_added_time    | entity_id | state_id       | .... | +---------------------+-----------+----------------+      | | 2015-05-15 14:24:28 |         1 |              3 |      | | 2015-05-15 14:24:30 |         2 |              3 |      | | 2015-05-15 13:29:44 |         3 |              2 |      | .......

that is, know last state change took place each entity before or @ given time. interval between state change not fixed. cannot have 2 time boundaries , find rows between them.

i have tried using timediff failed desired output. please guide me on path should take?

edit: quick responses. tried answers , noticed queries take quite lot of time fetch rows when executed on actual database. because fields entity_id , state_id foreign keys 2 other tables. known there way improve performance of query?

you can using variables:

select entity_id, state_added_time, state_id (   select state_added_time, state_id,           @row_number:= case when @entity = entity_id @row_number+1                              else 1                         end row_number,           @entity:=entity_id entity_id      state_history   state_added_time <= '2015-05-15 14:25:00' order entity_id, state_added_time desc ) t t.row_number = 1

@row_number being reset each time new entity_id encountered. within each entity_id, value of @row_number = 1 points recent record.

sql fiddle demo


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