Question

sql 查询union是如果两个表所查询的两个表中列的数量不一样 如何处理

select a , b , c , d from table1
union
select a , b from table2

由于两个表所要查询出的列的数量不一样 怎样才能显示出来呢
不想要有空的列

Answer 1

select a , b , c , d from table1
union
select a , b , '1', '2' from table2

Answer 2

select a,b,c,d from table1
union
select a,b,'','' from table2

Answer 3

select * from table1 a where not exists (select 1 from table2 b where a.a <> b.a and a.b<>b.b and a.c <> b.c)