Mysql子查詢及優化

子查詢：當一個查詢是另外一個查詢的子部分時，稱之爲子查詢。mysql create table t1(k1 int PRIMARY key,c1 int); create table t2(k2 int PRIMARY key,c2 int); insert into t2 values(1,10),(2,2),(3,30); mysql> SELECT t1.c1, (SELECT t2.c2

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