mysql union 组合查询

mysql> select * from test
    -> ;
+----+------------+-------+-----------+
| id | name       | score | subject   |
+----+------------+-------+-----------+
|   | xiaoming   |     | shuxue    |
|   | xiaohong   |     | shuxue    |
|   | xiaohong   |     | english   |
|   | xiaohong   |     | physics   |
|   | xiaohong   |     | astronaut |
|   | xiaoming   |     | physics   |
|   | xiaoming   |     | astronaut |
|   | xiaoming   |     | english   |
|   | xiaobai    |     | astronaut |
|  | .2xiaobai |     | english   |
|  | .2xiaobai |     | physics   |
|  | 3xiaobai   |     | shuxue    |
|  | 123xiaohei |     | astronaut |
|  | xiaohei    |     | shuxue    |
|  | xiaohei    |     | physics   |
|  | .12xiaohei |     | english   |
+----+------------+-------+-----------+
 rows in set (0.00 sec)

mysql> select * from user;
+------+----------+-----------+
| id   | name     | address   |
+------+----------+-----------+
|     | xiaoming | beijing   |
|     | xiaobai  | shandong  |
|     | xiaohong | suzhou    |
|     | xiaohei  | changchun |
+------+----------+-----------+
 rows in set (0.00 sec)

mysql> select id,name from user where name="xiaohong" union select id,name from test where name="xiaoming";
+------+----------+
| id   | name     |
+------+----------+
|     | xiaohong |
|     | xiaoming |
|     | xiaoming |
|     | xiaoming |
|     | xiaoming |
+------+----------+
 rows in set (0.00 sec)

mysql> select id,name from user where name="xiaohong" union all select id,name from test where name="xiaoming";
+------+----------+
| id   | name     |
+------+----------+
|     | xiaohong |
|     | xiaoming |
|     | xiaoming |
|     | xiaoming |
|     | xiaoming |
+------+----------+
 rows in set (0.00 sec)

mysql> select id,name from user where name="xiaohong" union all select id,name from test where name="xiaoming" order by id;
+------+----------+
| id   | name     |
+------+----------+
|     | xiaoming |
|     | xiaohong |
|     | xiaoming |
|     | xiaoming |
|     | xiaoming |
+------+----------+
 rows in set (0.00 sec)