我使用Linqer将SQL转换为LinQ,但结果与My SQL查询不一样:
Select ChuyenNganh.ChuyenNganhID,ChuyenNganh.TenChuyenNganh,SoLuong= count(BaiBao.ChuyenNganhID )
from BaiBao right join ChuyenNganh on ChuyenNganh.ChuyenNganhID = BaiBao.ChuyenNganhID
group by ChuyenNganh.ChuyenNganhID, ChuyenNganh.TenChuyenNganh
转换为Linq
var queryChuyenNganh = from t in myPhanLoaiTaiLieuDataContext.ChuyenNganhs
join t0 in myPhanLoaiTaiLieuDataContext.BaiBaos on new { ChuyenNganhID = t.ChuyenNganhID } equals new { ChuyenNganhID = Convert.ToInt32(t0.ChuyenNganhID) } into t0_join
from t0 in t0_join.DefaultIfEmpty()
group t by new
{
t.ChuyenNganhID,
t.TenChuyenNganh
} into g
select new
{
ChuyenNganhID = (System.Int32)g.Key.ChuyenNganhID,
g.Key.TenChuyenNganh,
SoLuong =(Int32)g.Count()
};
结果:
LINQ
SQL
谁能为我解决这个问题?
很可能SQL查询可以在没有group by
的LINQ中重写,而是简单的LINQ GroupJoin
。
但转换的主要问题是SQL COUNT(expr)
不计算NULL
值,并且没有直接的LINQ等价物,因此需要条件Count
或Sum
(我个人更喜欢后者,因为通常它转换为更好的SQL)。
因此,您查询所需的最小更改是
group t by new
到group t0 by new
和SoLuong =(Int32)g.Count()
到SoLuong = g.Sum(t0 => t0 != null ? 1 : 0)
附:正如开头所提到的,我将尝试以下LINQ查询:
var queryChuyenNganh =
from t in myPhanLoaiTaiLieuDataContext.ChuyenNganhs
join bb in myPhanLoaiTaiLieuDataContext.BaiBaos
on t.ChuyenNganhID equals bb.ChuyenNganhID into t_BaiBaos
select new
{
t.ChuyenNganhID,
t.TenChuyenNganh,
SoLuong = t_BaiBaos.Count()
};
区别在于SQL在BaiBao.ChuyenNganhID
(外连接表中的列)中计算非空值,而LINQ计算所有记录。
您还需要使LINQ计数非空值:
var queryChuyenNganh = from t in myPhanLoaiTaiLieuDataContext.ChuyenNganhs
join t0 in myPhanLoaiTaiLieuDataContext.BaiBaos
on new { t.ChuyenNganhID } equals new { ChuyenNganhID = Convert.ToInt32(t0.ChuyenNganhID) } into t0_join
from t0 in t0_join.DefaultIfEmpty()
group new {T=t, NonNull=t0.ChuyenNganhID != null} by new
{
t.T.ChuyenNganhID,
t.T.TenChuyenNganh
} into g
select new
{
ChuyenNganhID = (System.Int32)g.Key.ChuyenNganhID,
g.Key.TenChuyenNganh,
SoLuong =(Int32)g.Count(x => x.NonNull)
};