t1
t2
t3
t4
目标：将t1,t3,t4的表内容合并到t2中
/*插入只有t1有的内容*/ insert into t2 (a,b) SELECT * from t1 where not EXISTS( SELECT * from t3 where t1.a=t3.a )AND not EXISTS( SELECT * from t4 where t1.a=t4.a ); /*插入只有t1和t4有的内容*/ insert into t2 (a,b,c,f) SELECT t1.a,t1.b,t4.c,t4.f from t1,t4 where not EXISTS( SELECT * from t3 where t1.a=t3.a )and t1.a=t4.a; /*插入只有t2有的内容*/ insert into t2 (a,c,d,e) SELECT * from t3 where not EXISTS( SELECT * from t1 where t3.a=t1.a )AND not EXISTS( SELECT * from t4 where t3.a=t4.a ); /*插入只有t1,t3有的内容*/ insert into t2 (a,b,c,d,e) SELECT t1.a,t1.b,t3.c,t3.d,t3.e from t1,t3 where not EXISTS( SELECT * from t4 where t1.a=t4.a )and t1.a=t3.a; /*插入只有t4有的内容*/ insert into t2 (a,c,f) SELECT * from t4 where not EXISTS( SELECT * from t1 where t4.a=t1.a )AND not EXISTS( SELECT * from t3 where t4.a=t3.a ); /*插入只有t3,t4有的内容*/ insert into t2 (a,c,d,e,f) SELECT t3.a,t3.c,t3.d,t3.e,t4.f from t4,t3 where not EXISTS( SELECT * from t1 where t1.a=t4.a )and t4.a=t3.a; /*插入都有的内容*/ insert into t2 (a,b,c,d,e,f) SELECT t1.a,t1.b,t3.c,t3.d,t3.e,t4.f FROM t1,t3,t4 where t1.a=t3.a and t1.a=t4.a;
最后
t2
