记录 C#中 LINQ 和 SQL 语句 的一些操作数据集合方法

 2022年03月11日：C# 中的语言集成查询 (LINQ) | Microsoft Docs 微软官网文档 内容翔实，本土化支持友好 哈哈哈哈哈

1，等效于sql  left join的LINQ语法：

 

 

2，

# 分组 求数量
SELECT  Column1 ,COUNT(*) AS aCount FROM 
( 
SELECT * FROM tableName

 ) AS T1 
GROUP BY Column1 #要和上面的Column1 一样 

ORDER BY aCount DESC ;

　　分组求数量 linq语法。

                     from d in _deviceEntities
                       group d by d.OperationCompanyName
                                into g
                       select new { Brand = g.Key, Count = g.Count()

 

SELECT code,StartTime,EndTime ,COUNT(DISTINCT StartTime) as Count FROM (
SELECT * FROM tablename
WHERE projectTypeName = '道路' AND StartTime >= '2021-07-05 00:00:00' AND EndTime <= '2021-07-05 23:59:59' AND TimeType = 1
GROUP BY Code,StartTime,EndTime 
 ORDER BY code DESC
) AS T
GROUP BY code
ORDER BY Count DESC;