从另一个表返回单个记录，每个事务具有多个记录

Question

如何创建一个查询，该查询将基于LoanApplicationDate返回最新的Soa LoanableAmount。

例如： 对于LoanID = 1，我想获取SoaID = 2的Soa记录，因为这是此LoanApplicationDate的最新可贷金额-2017-07-01。

到目前为止，这是我已经完成的事情：

select * 
  from Loan L
  join Soa S
    ON S.EmployeeID = L.EmployeeID
where S.TransactionDate <= L.LoanApplicationDate

为说明我要完成的工作，请参见下面的屏幕截图。

https://www.db-fiddle.com/f/3PBossUJLYQTQZJfZymiph/0

Answer 1

我认为您需要为联接设置条件：

select  
  L.LoanID,
  L.EmployeeID,
  L.LoanAmount,
  L.LoanApplicationDate,
  S.LoanableAmount,
  S.TransactionDate
from Loan L join Soa S
ON S.EmployeeID = L.EmployeeID and
S.TransactionDate = (select max(TransactionDate) from Soa where TransactionDate <= L.LoanApplicationDate)

请参见demo

Answer 2

SQL DEMO

select * 
from Loan L
join Soa S
  ON S.EmployeeID = L.EmployeeID 
 and S.TransactionDate = 
        (select max(S2.TransactionDate) 
         from Soa S2
         where S2.TransactionDate <= L.LoanApplicationDate
           and S2.`EmployeeID` = L.`EmployeeID`
        )

Answer 3

我认为您需要doc，然后进行过滤以获取最新日期：

join

Answer 4

以下查询将为您提供所有雇员ID，并在最近日期提取可贷金额

     Select employee_id, 
       LoanableAmount 
      transactionDate from table 
     having
  transactionDate=max(transactionDate)
    group by employee_id

Answer 5

您需要为每行运行一个子查询：

select q.*, S.LoanableAmount, S.TransactionDate from
   (select  
     L.*
     ,(select SoaID from Soa  x where x.EmployeeID = L.EmployeeID and x.TransactionDate <= L.LoanApplicationDate order by TransactionDate DESC limit 1) as SoaID 
   from Loan L) q
join Soa S on S.SoaID = q.SoaID

第4行将为您提供Soa表中行的SoaID，该行的最新日期小于或等于“申请日期”，然后使用该ID进行联接并显示其余字段。