MySQL教程58-IN和NOT IN用法詳解
阿新 • • 發佈:2020-08-19
MySQL中的 IN 運算子用來判斷表示式的值是否位於給出的列表中;如果是,返回值為 1,否則返回值為 0。
NOT IN 的作用和 IN 恰好相反,NOT IN 用來判斷表示式的值是否不存在於給出的列表中;如果不是,返回值為 1,否則返回值為 0。
IN 和 NOT IN 的語法格式如下:
expr IN ( value1, value2, value3 ... valueN ) expr NOT IN ( value1, value2, value3 ... valueN )
expr 表示要判斷的表示式,value1, value2, value3 ... valueN 表示列表中的值。MySQL 會將 expr 的值和列表中的值逐一對比。
【例項1】在 SQL 語句中使用 IN 和 NOT IN 運算子:
mysql> SELECT 2 IN (1,3,5,'thks'),'thks' IN (1,3,5, 'thks'); +---------------------+---------------------------+ | 2 IN (1,3,5,'thks') | 'thks' IN (1,3,5, 'thks') | +---------------------+---------------------------+ | 0 | 1| +---------------------+---------------------------+ 1 row in set, 2 warnings (0.00 sec) mysql> SELECT 2 NOT IN (1,3,5,'thks'),'thks' NOT IN (1,3,5, 'thks'); +-------------------------+-------------------------------+ | 2 NOT IN (1,3,5,'thks') | 'thks' NOT IN (1,3,5, 'thks') | +-------------------------+-------------------------------+| 1 | 0 | +-------------------------+-------------------------------+ 1 row in set, 2 warnings (0.00 sec)
由結果可以看到,IN 和 NOT IN 的返回值正好相反。
對空值 NULL 的處理
當 IN 運算子的兩側有一個為空值 NULL 時,如果找不到匹配項,則返回值為 NULL;如果找到了匹配項,則返回值為 1。
請看下面的 SQL 語句如下:
mysql> SELECT NULL IN (1,3,5,'thks'),10 IN (1,3,NULL,'thks'); +------------------------+-------------------------+ | NULL IN (1,3,5,'thks') | 10 IN (1,3,NULL,'thks') | +------------------------+-------------------------+ | NULL | NULL | +------------------------+-------------------------+ 1 row in set, 1 warning (0.00 sec) mysql> SELECT NULL IN (1,3,5,'thks'),10 IN (1,10,NULL,'thks'); +------------------------+--------------------------+ | NULL IN (1,3,5,'thks') | 10 IN (1,10,NULL,'thks') | +------------------------+--------------------------+ | NULL | 1 | +------------------------+--------------------------+ 1 row in set (0.00 sec)
NOT IN 恰好相反,當 NOT IN 運算子的兩側有一個為空值 NULL 時,如果找不到匹配項,則返回值為 NULL;如果找到了匹配項,則返回值為 0。
請看下面的 SQL 語句如下:
mysql> SELECT NULL NOT IN (1,3,5,'thks'),10 NOT IN (1,0,NULL,'thks'); +----------------------------+-----------------------------+ | NULL NOT IN (1,3,5,'thks') | 10 NOT IN (1,0,NULL,'thks') | +----------------------------+-----------------------------+ | NULL | NULL | +----------------------------+-----------------------------+ 1 row in set, 1 warning (0.00 sec) mysql> SELECT NULL NOT IN (1,3,5,'thks'),10 NOT IN (1,10,NULL,'thks'); +----------------------------+------------------------------+ | NULL NOT IN (1,3,5,'thks') | 10 NOT IN (1,10,NULL,'thks') | +----------------------------+------------------------------+ | NULL | 0 | +----------------------------+------------------------------+ 1 row in set (0.00 sec)