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Is there a big performance difference between those two sql count statements, when performing large counts (large here means 100k + records)
first:
SELECT count(*) FROM table1 WHERE <some very complex conditions>
second:
SELECT count(*) FROM (SELECT * FROM table1 WHERE <some very complex conditions>) subquery_alias
I know that first approach is right, but i want to know is this statements will perform similar ?
The query optimizer will most likely transform your second query into the first one. There should be no measurable performance difference between those two queries.