Question

我有这个SQL查询，如果从Oracle数据库中的TOAD执行，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() };

然后你可以用连接

进行正常选择

 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, ...}

Answer 2

要进行左连接，请修改@ SAJ答案，如下所示：

var result =  from technician in Technicians
   join txn in txnDetails on technician.TechnicianCode equals 
    txn.TechnicianCode
   into j 
   from lj in j.DefaultIfEmpty()
 select lj;

Answer 3

这是你在找？

var result = from technician in Technicians
                join job in Jobs on technician.TechnicianCode equals job.TechnicianCode into A
                from job in A.DefaultIfEmpty()
                where job.TxnCode == "Jc" || job.TxnCode == "Jcd"
                select new 
                {
                    Tech = technician,
                    Job = job
                };

要获得计数，您只需使用：

var count = result.Where(r => r.Job != null).Count();

Answer 4

尝试代码：

var result= (from  p in Technicians            
             join q in Jobs.where(c=>c.TxnCode=="JC" || c.TxnCode==c."Jcd").GroupBy(c=>c.TechnicianCode)
             .Select(m => new { jobcount = m.Count(), TechnicianCode = m.FirstOrDefault().TechnicianCode,  TxnCode=m.FirstOrDefault().TxnCode}).ToList()             
             on p.TechnicianCode equals q.TechnicianCode into jj from kk in jj.DefaultIfEmpty() 
             select new {    
                          jobcount=kk.jobcount,  
                          TxnCode=kk.TxnCode, 
                          TechnicianCode=p.TechnicianCode 
                        }).ToList();

带连接和计数的快速linq查询

4 个答案: