mysql union 组合查询

mysql> select * from test
    -> ;
+----+------------+-------+-----------+
| id | name       | score | subject   |
+----+------------+-------+-----------+
|  1 | xiaoming   |    89 | shuxue    |
|  2 | xiaohong   |    89 | shuxue    |
|  3 | xiaohong   |    80 | english   |
|  4 | xiaohong   |    80 | physics   |
|  5 | xiaohong   |    80 | astronaut |
|  6 | xiaoming   |    80 | physics   |
|  7 | xiaoming   |    80 | astronaut |
|  8 | xiaoming   |    80 | english   |
|  9 | xiaobai    |    80 | astronaut |
| 10 | 1.2xiaobai |    80 | english   |
| 11 | 2.2xiaobai |    80 | physics   |
| 12 | 3xiaobai   |    80 | shuxue    |
| 13 | 123xiaohei |    80 | astronaut |
| 14 | xiaohei    |    80 | shuxue    |
| 15 | xiaohei    |    80 | physics   |
| 16 | .12xiaohei |    80 | english   |
+----+------------+-------+-----------+
16 rows in set (0.00 sec)



mysql> select * from user;
+------+----------+-----------+
| id   | name     | address   |
+------+----------+-----------+
|    1 | xiaoming | beijing   |
|    2 | xiaobai  | shandong  |
|    3 | xiaohong | suzhou    |
|    4 | xiaohei  | changchun |
+------+----------+-----------+
4 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     |
+------+----------+
|    3 | xiaohong |
|    1 | xiaoming |
|    6 | xiaoming |
|    7 | xiaoming |
|    8 | xiaoming |
+------+----------+
5 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     |
+------+----------+
|    3 | xiaohong |
|    1 | xiaoming |
|    6 | xiaoming |
|    7 | xiaoming |
|    8 | xiaoming |
+------+----------+
5 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     |
+------+----------+
|    1 | xiaoming |
|    3 | xiaohong |
|    6 | xiaoming |
|    7 | xiaoming |
|    8 | xiaoming |
+------+----------+
5 rows in set (0.00 sec)