2020-03-31
阅读量:
725
MySQL：先连纵向，再连横向，可行吗？
答：可行，如下面例子：
create database test;
use test;
create table t1(
a int,
b int);
create table t2(
a int,
b int);
create table t3(
a int,
c int);
insert t1 values(1,1),(2,2);
insert t2 values(3,3),(4,4);
insert t3 values(1,11),(2,22),(3,33),(4,44);
(select * from t1) union (select * from t2);
select * from t3 left join ((select * from t1) union (select * from t2)) as t4 on t3.a = t4.a;
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