如何将sql查询更改为linq?
如何将此sql查询更改为linq?我有三个连接,最后一个连接是selectquery如何将sql查询更改为linq?,sql,linq,sql-to-linq-conversion,Sql,Linq,Sql To Linq Conversion,如何将此sql查询更改为linq?我有三个连接,最后一个连接是selectquery 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
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
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:
我根据以下评论修改了我的答案:
此方法将导致较大数据集出现问题,因为 从tblMets和tblMods获取每条记录,并从 数据库进入内存
此方法将导致较大数据集出现问题,因为您将来自数据库的tblMets、tblMods和tblGroupDatas的每条记录都存储到内存中。您可以使用DB实体直接查询数据库:var query1=from grp in ctnx.tblMets group grp by grp.MetID_FK into g let maxId=g.Max(gId=>gId.GroupDataID)选择new{MetID=g.Key,maxId}@Luc,u r完全正确,但这不是性能问题,我想展示如何逐步完成sql到linq的转换。@Luc非常感谢。我使用你的解决方案。