sql - 在 Linq 中加入子查询结果

Question

我又提出了一个疑问：有没有一种方法可以让我们使用一个查询的结果，然后像在 SQL 中那样进一步加入相同的查询：

SELECT Applications.* , ApplicationFees.ApplicationNo, ApplicationFees.AccountFundDate1,ApplicationFees.AccountFundDate2 ,ApplicationFees.AccountFundDate3 , ApplicationFees.AccountCloseDate1, ApplicationFees.AccountCloseDate2,ApplicationFees.AccountCloseDate3,
isnull(SUBQRY11.AMNT ,0) as SCMSFEE1R,
isnull(SUBQRY12.AMNT,0) as SCMSFEE2R,
Left Join 
(
SELECT ApplicationNo,COUNT(ApplicationNo) AS CNT, SUM(Amount) as AMNT 
FROM Payments where (FEETYPE=1 AND FeePosition=1)  and (FeeDate>='2011-01-01')
and (FeeDate<='2012-01-01')
GROUP BY ApplicationNo
)SUBQRY11
ON ApplicationFees.ApplicationNo= SUBQRY11.ApplicationNo 
Left Join 
(
SELECT ApplicationNo,COUNT(ApplicationNo) AS CNT2, SUM(Amount) as AMNT 

FROM Payments where (FEETYPE=1 AND FeePosition=2) and (FeeDate>='2011-01-01') 
 and (FeeDate<='2012-01-01')
GROUP BY ApplicationNo )SUBQRY12 ON ApplicationFees.ApplicationNo=SUBQRY12.ApplicationNo

我想避免在 foreach 中进行相同的查询，因为这将非常耗时。

Answer 1

是的，您可以加入子查询。像这样：

var query = from f in db.ApplicationFees
            join sub in (from p in db.Payments
                         where p.Type == 1 && p.Position == 1 && 
                               p.Date >= fromDate && p.Date <= toDate
                         group p by p.ApplicationNo into g
                         select new {
                              ApplicationNo = g.Key,
                              CNT = g.Count(),
                              AMNT = g.Sum(x => x.Amount)
                         }) 
           on f.ApplicationNo equals sub.ApplicationNo into feePayments
           select new { Fee = f, Payments = feePayments };

但是在单个查询中编写它不是很容易维护。考虑从单独定义的子查询中组合查询：

var payments = from p in db.Payments
               where p.Type == 1 && p.Position == 1 && 
               p.Date >= fromDate && p.Date <= toDate
               group p by p.ApplicationNo into g
               select new {
                    ApplicationNo = g.Key,
                    CNT = g.Count(),
                    AMNT = g.Sum(x => x.Amount)
              };

var query = from f in db.ApplicationFees
            join p in payments 
               on f.ApplicationNo equals p.ApplicationNo into feePayments
            select new { Fee = f, Payments = feePayments };