当查询条件为空时 想让 sql 中的 查询条件无效 该如何实现 sql 语句如下。。SELECT b.*,CONCAT(date_format(b.STARTTIME,'%Y年%c月%d日' ),'-',date_format(b.STARTTIME,'%Y年%c月%d日' )) as worktime FROM tb_yhzy_mainproject b where where date_format(b.UPPERDATE,'%Y-%c-%d' )<'${endtime}' and date_format(b.UPPERDATE,'%Y-%c-%d' )>'${starttime}' and b.PROJECTNAME = '${projectname}'and b.ORGNO= '${orgno}' b.BUILDER = '${WORKNAME}'