sql条件查询-

使用like,实现模糊查询，子查询
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SELECT
            MAX( ctime ) AS max_ctime
        FROM
            ( SELECT ctime FROM alarm_monitor WHERE alarm_status = 'true' AND is_under like '%0' ) as a
使用自定义值，默认查询所有
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set @pos=""
select * from user where (name=@pos or @pos="")