IN子句
您可以使用IN子句替换许多OR条件，要了解IN子句， 假设有一个employee_tbl表，该表具有以下记录-
mysql> SELECT * FROM employee_tbl;
+------+------+------------+--------------------+
| id | name | work_date | daily_typing_pages |
+------+------+------------+--------------------+
| 1 | John | 2007-01-24 | 250 |
| 2 | Ram | 2007-05-27 | 220 |
| 3 | Jack | 2007-05-06 | 170 |
| 3 | Jack | 2007-04-06 | 100 |
| 4 | Jill | 2007-04-06 | 220 |
| 5 | Zara | 2007-06-06 | 300 |
| 5 | Zara | 2007-02-06 | 350 |
+------+------+------------+--------------------+
7 rows in set (0.00 sec)
现在，假设基于上表，您要显示的daily_typing_pages分别等于250、220和170的记录。这可以使用OR条件进行如下操作
mysql>SELECT * FROM employee_tbl
->WHERE daily_typing_pages= 250 OR
->daily_typing_pages= 220 OR daily_typing_pages= 170;
+------+------+------------+--------------------+
| id | name | work_date | daily_typing_pages |
+------+------+------------+--------------------+
| 1 | John | 2007-01-24 | 250 |
| 2 | Ram | 2007-05-27 | 220 |
| 3 | Jack | 2007-05-06 | 170 |
| 4 | Jill | 2007-04-06 | 220 |
+------+------+------------+--------------------+
4 rows in set (0.02 sec)
使用IN子句可以实现以下相同效果
mysql> SELECT * FROM employee_tbl
-> WHERE daily_typing_pages IN ( 250, 220, 170 );
+------+------+------------+--------------------+
| id | name | work_date | daily_typing_pages |
+------+------+------------+--------------------+
| 1 | John | 2007-01-24 | 250 |
| 2 | Ram | 2007-05-27 | 220 |
| 3 | Jack | 2007-05-06 | 170 |
| 4 | Jill | 2007-04-06 | 220 |
+------+------+------------+--------------------+
4 rows in set (0.02 sec)
