1.3.4.3 检索部分数据列

如果您不想看到表中的全部数据列，仅只想看到 name 、birth ，那么您可以这样操作：

mysql> SELECT name, birth FROM pet;
+----------------------+------------+
| name                 | birth      |
+----------------------+------------+
| Fluffy               | 1993-02-04 |
| Claws                | 1994-03-17 |
| Buffy                | 1989-05-13 |
| Fang                 | 1990-08-27 |
| Bowser               | 1989-08-30 |
| Chirpy               | 1998-09-11 |
| Whistler             | 1997-12-09 |
| Slim                 | 1996-04-29 |
| Puffball             | 1999-03-30 |
+----------------------+------------+
9 rows in set (0.00 sec)

如果您只想看到宠物的 owner ：

mysql> SELECT owner FROM pet;
+--------+
| owner  |
+--------+
| Harold |
| Gwen   |
| Harold |
| Benny  |
| Diane  |
| Gwen   |
| Gwen   |
| Benny  |
| Diane  |
+--------+
9 rows in set (0.01 sec)

上面的例子中 owner 重复出现多个，如果您仅想结果中出现一次，那么您可以使用 DISTINCT 关键字。

mysql> SELECT DISTINCT owner FROM pet;
+--------+
| owner  |
+--------+
| Harold |
| Gwen   |
| Benny  |
| Diane  |
+--------+
4 rows in set (0.00 sec)

使用 where

mysql> SELECT name, species, birth FROM pet
    -> WHERE species = 'dog' OR species = 'cat';
+----------------------+---------+------------+
| name                 | species | birth      |
+----------------------+---------+------------+
| Fluffy               | cat     | 1993-02-04 |
| Claws                | cat     | 1994-03-17 |
| Buffy                | dog     | 1989-05-13 |
| Fang                 | dog     | 1990-08-27 |
| Bowser               | dog     | 1989-08-30 |
+----------------------+---------+------------+
5 rows in set (0.00 sec)