1)請優(yōu)化： select a.key,a.value from a where a.key not in (select b.key from b)

　　2)已優(yōu)化： select t1.key,t1.value from ( select a.key,a.value from a ) t1 right join ( select b.key from b ) t2 on t1.key = t2 .key where t1.key is null;

　　3)請優(yōu)化： select a.key,a.value from a where a.key in (select b.key from b)

　　4)已優(yōu)化： select t1.key,t1.value from ( select a.key,a.value from a ) t1 join ( select b.key from b ) t2 on t1.key = t2 .key;

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