如下面两个查询所示,我们发现它们都很好.然后我很困惑为什么我们应该使用BETWEEN,因为我发现BETWEEN在不同的数据库中的行为与
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- SELECT *
- FROM employees
- WHERE salary BETWEEN 5000 AND 15000;
- SELECT *
- FROM employees
- WHERE salary >= 5000
- AND salary <= 15000;
解决方法
BETWEEN可以帮助避免不必要的重新评估表达式：
- SELECT AVG(RAND(20091225) BETWEEN 0.2 AND 0.4)
- FROM t_source;
- ---
- 0.1998
- SELECT AVG(RAND(20091225) >= 0.2 AND RAND(20091225) <= 0.4)
- FROM t_source;
- ---
- 0.3199
t_source只是一个具有1,000,000条记录的虚拟表.
当然,BETWEEN更可读.在查询中使用它需要3次才能永远记住语法.
在sql Server和MysqL中,对一个具有非领先’％’的常量的LIKE也是一对> =和< ;:
- SET SHOWPLAN_TEXT ON
- GO
- SELECT *
- FROM master
- WHERE name LIKE 'string%'
- GO
- SET SHOWPLAN_TEXT OFF
- GO
- |--Index Seek(OBJECT:([test].[dbo].[master].[ix_name_desc]),SEEK:([test].[dbo].[master].[name] < 'strinH' AND [test].[dbo].[master].[name] >= 'string'),WHERE:([test].[dbo].[master].[name] like 'string%') ORDERED FORWARD)
但是,LIKE语法更清晰.
