可以使用IN子句來取代許多OR條件
要了解IN子句,考慮下面的 employee_tbl 表,它有以下記錄:
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)
現在上面的基礎上,假設要在上表中顯示 daily_typing_pages 等於 250,220 和 170 的記錄。這可以通過使用OR條件進行查詢如下:
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)
同樣可以使用 IN 子句來實現如下:
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)