linq用lambda表达式 left join 自连接怎么写

Posted 2023-04-13

参考技术A .问题解决
通过以上分析，将''改为NULL，问题得到有效解决或者把谓词写到每个子SQL里面。当然，只要是非''的都是可以的，比如' '(空格）。

dingjun123@ORADB> SELECT *
2 FROM (SELECT t1.subobject_name, t1.object_name, t1.object_type
3 FROM t1
4 UNION ALL
5 SELECT NULL, t2.object_name, t2.object_type
6 FROM t2
7 UNION ALL
8 SELECT t3.subobject_name, NULL, t3.object_type FROM t3) t
9 WHERE (t.subobject_name = 'T' OR t.object_name = 'T');

256 rows selected.
Elapsed: 00:00:00.72

Execution Plan
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Plan hash value: 3324794093
---------------------------------------------------------------------本回答被提问者和网友采纳

Linq 多连接及 left join 实例 记录

var retList = from d in mbExList.Cast<MaterialBaseEx>().ToList()
join c in umcList.Cast<ClassifyBaseEx>().ToList() on d.ClsCode equals c.ClsCode
join b in collectItem.Cast<CollectItem>().ToList() on d.Guid equals b.MatID into temp
join e in mlpList.Cast<MaterialLastPrice>().ToList() on d.MatCode equals e.MatCode into tempxx
from tt in temp.DefaultIfEmpty()
from xx in tempxx.DefaultIfEmpty()
where (d.IsPublish.Equals(true)) || tt != null
select new MaterialPriceCollect
{
Guid = Guid.NewGuid().ToString(),
MatCode = d.MatCode,
//Area = areaRec.Text,
PriceType = 1,
State = 2,
MatName = d.MatName==null?"":d.MatName,
Unit = d.MatUnit == null ? "" : d.MatUnit,
MatType = d.MatModel == null ? "" : d.MatModel,
LastPrice = (xx==null || xx.LastPrice == null) ? 0 : xx.LastPrice,
UserId = "_" + userId + ",",
MatId = d.Guid == null ? "" : d.Guid,
IsFrequently = (int)EumIsFrequently.否,
//ReportTime = DateTime.Now,
Weight = (tt==null ||tt.Weight == null) ? 1 : tt.Weight,
//AreaCode = areaRec.Id,
//PeriodNo = objMat.CurPeriodNo,
};