IN
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语法格式:
expr IN (value,...)
说明:
如果表达式等于括号内任意一个表达式的值，返回1，否则返回0。如果所有参数都是常量，会将表达式按照类型进行分类。in匹配是通过二分法搜索实现的。这就意味着：如果in 内的参数全是常量，那么搜索就非常的快。另一方面,如果有类型转换，则会依照 Type Conversion的标准将所有参数进行类型转换。
例子:
MariaDB [(none)]> SELECT 2 IN (0,3,5,7); +----------------+ | 2 IN (0,3,5,7) | +----------------+ | 0 | +----------------+
MariaDB [(none)]> SELECT 'wefwf' IN ('wee','wefwf','weg');
+----------------------------------+
| 'wefwf' IN ('wee','wefwf','weg') |
+----------------------------------+
| 1 |
+----------------------------------+
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