记录 C#中 LINQ 和 SQL 语句 的一些操作数据集合

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 ;

　　

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;