1.表关联查询

SQL语法_mysql
案例一：三张表做关联查询案例如下：

  select sald.assetId,a.cpu,a.machineryDisk,a.solidDisk,s.name,sald.lendTime,sald.returnTime from StaffAssetLendDetail  sald  join staff s
        on sald.staffId=s.id  join asset a on a.assetId=sald.assetId where 1=1
        <if test="staffId!= null">
            and sald.staffId=#{staffId}
        </if>
        <if test="assetId!=null">
            and sald.assetId=#{assetId}
        </if>