使用左右连接和嵌套查询对 linq 进行 SQL 查询答案

【问题标题】：SQL query to linq with right and left joins and nested query使用左右连接和嵌套查询对 linq 进行 SQL 查询
【发布时间】：2013-12-02 16:47:49
【问题描述】：

我的sql查询是

SELECT DISTINCT 
  tblProjects.RevID, tblProjects.CEQRNum, tblProjects.ProjectName, GEOCODE.BBL,     tblProjects.BoroID, GEOCODE.BLOCK, GEOCODE.LOT, 
                     tblMilestoneType.MilestoneName, tblMilestone.MilestoneDate
FROM            tblMilestoneType INNER JOIN
                     tblMilestone ON tblMilestoneType.MilestoneID = tblMilestone.MilestoneTypeID RIGHT OUTER JOIN
                     tblProjects ON tblMilestone.RevID = tblProjects.RevID LEFT OUTER JOIN
                     GEOCODE ON tblProjects.RevID = GEOCODE.RevID
WHERE        (
            tblMilestone.MilestoneDate IN (SELECT MAX(tblMilestone.MilestoneDate) AS MilestoneDate
                                          FROM tblMilestone INNER JOIN tblMilestoneType ON tblMilestone.MilestoneTypeID = tblMilestoneType.MilestoneID
                                          GROUP BY tblMilestone.RevID)
         )
ORDER BY tblProjects.RevID

我正在尝试将其转换为 linq。

所以我从

开始

projectList = db.tblMilestoneTypes
                                .Join(db.tblMilestones,
                                    mileType => mileType.MilestoneID,
                                    mile => mile.MilestoneTypeID,
                                    (mileType, mile) => new
                                    {
                                        tblMilestoneType = mileType,
                                        tblMilestone = mile
                                    })
                                .Join(db.tblProjects,                                        
                                    project => project.        // does not work)

也试过了

projectList = from MilestoneTypeTable in db.tblMilestoneTypes 
                          join MilestoneTable in db.tblMilestones  on MilestoneTypeTable.MilestoneID equals MilestoneTable.MilestoneTypeID
                          rig   // no right or left join.

我该怎么做尼哈

【问题讨论】：

stackoverflow.com/questions/9914623/… ...哦...看！
您的解决方案有什么问题？ “不起作用”的信息还不够。具体是什么不工作？
我的问题是如何在 linq 中进行左右连接和子查询

标签： c# sql linq

【解决方案1】：

你可以试试

projectList = from MilestoneTypeTable in db.tblMilestoneTypes
                      join MilestoneTable in db.tblMilestones on MilestoneTypeTable.MilestoneID equals MilestoneTable.MilestoneTypeID into MileStones 
from mileStone in MileStones 
join from projects in db.tblProjects
on mileStone.RevID  equals projects.RevID
select new { MileStoneType = MilestoneTypeTable, MileStones = mileStone , Project = projects };

【讨论】：

【解决方案2】：

嗯，经过大量的研发，这是我发现的

具有 LEFT OUTER JOIN 和 RIGHT OUTER JOIN 的 T-SQL 可以转换为仅具有 LEFT OUTER JOIN 的查询
将子查询作为连接的一部分

这是查询。

    var query = from ProjectTable in db.tblProjects
                        from GeoCodeTable in db.GEOCODEs.Where(geo => geo.RevID == ProjectTable.RevID).DefaultIfEmpty()
                        from MilestoneTable in db.tblMilestones.Where(mile => mile.RevID == GeoCodeTable.RevID && mile.MilestoneDate == db.tblMilestones.OrderBy(x => x.RevID).Select(x => x.MilestoneDate).Max()).DefaultIfEmpty()
                        from MilestomeTypeTable in db.tblMilestoneTypes.Where(mt => mt.MilestoneID == MilestoneTable.MilestoneTypeID).DefaultIfEmpty()
            select new
            {
                Milestone = MilestoneTable,
                Project = ProjectTable,
                GeoCode = GeoCodeTable,
                MilestomeType = MilestomeTypeTable 
            };

【讨论】：