Linq Not in
DataTable:

t:
id WR WR1
0 W01 W01
1 W02 null
2 W03 W03
3 W03 null
4 null null

查询 WR1中没有的WR：也就是

select WR from t
where WR not in (select WR1 from t)

用Linq怎么实现？
[解决办法]

var query=from dt in t.AsEnumerable()
          where !t.AsEnumerable().Select(x=>x.Field<string>("WR1")).Contains(dt.Field<string>("WR")) 
          select dt.Field<string>("WR");