这样写怎么不行
select sum(j.length),sum(d.length)
from (res_xl_gdgx x left join res_jkx_info j on j.ssgdgx = x.ssgdgx) left join res_dl_info d d.ssgdgx,0,21 = x.ssgdgx
where x.id = 'XIL0010494' group by x.Mc

这样sum(d.length)的结果怎么不准呢。。该怎么写呢，各位帮帮忙！ 完事请结贴