mysql数据库中的多表联查

在项目中遇见了mysql库的多表联查，记录下来，供以后查阅。

select a.slzgh as Zgh,c.username as Xm,a.slksh as Ksh,d.Ksmc,a.Ffdate,b.Sortid,b.Sortname,sum(b.Silnum) as Silnum
from offmate a
inner join offmatedetail b on a.contentid=b.contentid
left join user c on a.slzgh=c.userid
left join ks d on a.slksh=d.ksh  group by a.slzgh
where a.sflq=2 and b.sortid='"+sortid+"' and a.ffdate between '"+sdate+"' and '"+edate+"'"
前面两个表提供主要数据，后面两个表提供单项名称。
根据id号和日期区间来查询数据。