不用左连接只用参数的时候正常，反之也是，不知道该如何同时存在，求大神！！！

select id, event_date, event_time, event_type, pic_name, source_channel, opinion, concat ('D:/00code/LuzhengTongV2/',event_date,'/channel',source_channel,'/',pic_name) as url from lz_event as a

left join 

(select event_type,event_name from lz_event_code where event_level='2' ) as b  

on a.event_type =b.event_type

where  event_date='${date_select}' and source_channel='${channel_select}' order by source_channel, event_time desc