21 union(可以将查询结果集相加)
第一种:找出工作岗位是salesman和manager的员工?
select ename,sal from emp
union
select dname from dept;
ERROR 1222 (21000): The used SELECT statements have a different number of columns
21 union(可以将查询结果集相加)
第一种:找出工作岗位是salesman和manager的员工?
select ename,sal from emp
union
select dname from dept;
ERROR 1222 (21000): The used SELECT statements have a different number of columns