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HomeDatabaseMysql TutorialMYSQL必知必会读书笔记第七章之数据过滤_MySQL

mysql简介

MySQL是一种开放源代码的关系型数据库管理系统(RDBMS),MySQL数据库系统使用最常用的数据库管理语言--结构化查询语言(SQL)进行数据库管理。

计算次序:

where 可以包含任意数目的and和or,允许两者结合以进行复杂和高级的过滤。但是SQL在操作or之前会优先的处理AND操作符。如果想优先的使用or的条件可以使用括号。

in:为什么要使用in操作符?其优点具体如下。

1.在使用长的合法选项清单时,in操作符的语法更清楚直观

2.在使用IN时,计算的次序更容易管理(因为使用的操作符更少)

3.IN操作符一般比OR操作符执行更快

4.IN 最大的优点是可以包含其他SELECT语句,使得能够动态的建立WHERE子句。

MySQL中的NOT MYSQL支持使用NOT对IN 、BETWEEN和EXISITS子句取反,这与多数其他的DBMS允许使用NOT对各种条件取反有很大差别。

使用IN的优势。对于简单的where子句,使用NOT确实没有什么优势。但是在复杂的子句中,NOT是非常有用的。例如操作符联合使用时。NOT使找出与条件列表不匹配的行时非常简单的。

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