这样的sql怎么写啊?......................急的很哩!!

A表中的字段有
...sl(数量) , jldw(计量单位)....
要求:按计量单位的"吨","米","平方米"求sum(sl),
用一条sql语句实现,
求救啊,各位大虾!!
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select sum(SL),jldw from table
group by jldw
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select jldw, sum(sl) from tablename group by jldw