Oracle nested queries performance
I am trying to build a complex query which has two levels (one parent query having a nested query). In a very low level I have something like this: SELECT * from (SELECT a.1 a1, a.2 a2, a.3 a3, b.1 b1, b.2 b2, b.3 b3 from a join b on a.1 = b.1) sq where sq.b3 = '123' With this approach the query turns to take a lot of time while when doing like below is immediate... SELECT * from (SELECT a.1 a1, a.2 a2, a.3 a3, b.1 b1, b.2 b2, b.3 b3 from a join b on a.1 = b.1 where sq.b3 = '123') sq I understand that nested queries can affect the performance but I was expecting the optimizer to be able to "improve" it and bring more efficiency... The thing is that I need to use the first approach as in the parent query I am putting quite a lot of validations that cannot be placed in the nested query due to the big coplexity of it... What am wrong with?
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