c# - 具有连接和计数的快速 linq 查询

Question

如果从 Oracle 数据库中的 TOAD 执行，我有这个 SQL 查询运行速度很快，其中 Jobs 表包含超过 200 万条记录。

select * from Technicians  A
left join  
  (select TechnicianCode,count(*)JobCount from Jobs 
   where TxnCode in ('Jc','Jcd') group by TechnicianCode) B
on B.TechnicianCode =A.TechnicianCode

无法以有效的方式将其转换为 linq。 有人可以帮忙吗？

Answer 1

你可以试试这个

var txnDetails =  from job in jobs
                  where job.TxnCode == "Jc" || job.TxnCode == "Jcd"
                  group job by job.TechnicianCode into g
                  select new { TechnicianCode = g.Key, count = g.Count() };

然后你就可以用join做正常的select了

 from technician in Technicians
 join txn in txnDetails on technician.TechnicianCode equals 
   txn.TechnicianCode into tg
 from t in tg.DefaultIfEmpty()
 select new {Count = t==null? 0: t.count, ...}