java _sql union

• union 可以将查询结果集相加

//找出工作岗位是AAAA和BBB的员工
1.select name,job from t_user where job = 'AAAA' or job = 'BBB';
2.select name,job from t_user where job in('AAAA','BBB');
//把俩张查询结果相加
3.select name,job from t_user where job = 'AAAA' union select name,job from t_user where job = 'BBB';
+-----------+------+
| name      | job  |
+-----------+------+
| HanMeimei | AAAA |
| ZhangWei  | AAAA |
| Lucy      | BBB  |
| WeiHua    | BBB  |
+-----------+------+

• 俩张不相干的表中的数据拼接在一起显示

select name from t_user union select dname from dept;
+-----------+
| name      |
+-----------+
| Ann       |
| HanMeimei |
| Ka_te     |
| Lisa      |
| Lucy      |
| WeiHua    |
| ZhangWei  |
| ZWei      |
| 测试部    |
| 开发部    |
| 市场部    |
| 设计部    |
| 采购部    |