如何将 sql 查询更改为 linq？

Question

如何将此 sql 查询更改为 linq？我有三个连接，最后一个连接是 select 查询。

select  mod.ModSerial,
        met.MetSerial,
        met.WaterNo,
        met.PowerNo,
        Gro.GroupDate
     from MetlDB.dbo.tblMet AS met
     join MetDB.dbo.tblMod AS mod on mod.ModID= met.ModID_FK  
     join MetDB.dbo.tblGroupData As Gro on Gro.MetID_FK= met.MetID
     join(select MetID_FK,
           max(GroupDataID) as maxgroupdata
           from MetDB.dbo.tblGroupData
           group by MetID_FK) g on met.MetID=g.MetID_FK and Gro.GroupDataID=g.maxgroupdata

Answer 1

给你漂亮的：

    using (MetDBEntities ctnx = new MetDBEntities())
    {
        var query1 = from grp in ctnx.tblGroupDatas
                     group grp by grp.MetID_FK into g
                     let maxId = g.Max(gId => gId.GroupDataID)
                     select new { metId = g.Key, maxId };

        var query2 = from met in ctnx.tblMets
                     from mod in ctnx.tblMods.Where(mo => mo.ModId == met.ModId_fk)
                     from grp in ctnx.tblGroupDatas.Where(gr => gr.MetID_FK == met.MetId)
                     from q1 in query1.Where(q => q.metId == met.MetId && grp.GroupDataID == q.maxId)
                     select new { mod.ModSerial, met.MetSerial, met.Waterno, met.powerno, grp.GroupDate };

        var result = query2.ToList();
    }

编辑： 我根据这条评论修改了我的答案：

This methode is will cause problems with larger dataset, because you get every record from tblMets and tblMods and tblGroupDatas from the database into memory...

如何将 sql 查询更改为 linq？

how to change sql query to linq?

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linq

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