Question

假设有一个包含两个表的数据库，分别是“贷款”和“帐单支付”。

对于“贷款”表，我具有以下列：

loanId,
clientId(primary key),
DisbursementDate,
applicationDate,
approvalDate,
loanNumber,
loanAmount,
interestRate

Billpayment表列包括：

billId(primary),
customerId(foreign),
billAmount,
payment_status[success/fail],
billDate

如何获取在2018年3月支付账单的客户，并显示在2018年剩余月份中至少支付账单的客户数量，此外，还要显示是否账单付款客户是否在2018年内有贷款？

Answer 1

好的，让我们开始吧。我没有测试过任何一个，也没有对其进行适当的优化，但是希望它会有所帮助。

要列出2018年3月的付款，假设我们不在乎是否成功，请执行以下操作：

select * from billpayment
where month(billDate) = 3 and year(billDate) = 2018

要在上面包含相关的客户信息，请加入：

select * from billpayment
join loans on customerId = clientId
where month(billDate) = 3 and year(billDate) = 2018

要仅列出在2018年的另一个月内也进行过付款的客户，请再次加入派生表：

select * from billpayment b
join loans l on b.customerId = l.clientId
join (select distinct b1.clientId as clientid1 from billpayment b1
      where year(b1.billdate) = 2018 and month(b1.billdate) <> 3) c
        on b.customerId = c.clientId1 
where month(b.billDate) = 3 and year(b.billDate) = 2018

要检查他们是否在2018年开始贷款（假设申请日期为准），请在您的where子句中添加and：

select * from billpayment b
join loans l on b.customerId = l.clientId
join (select distinct b1.clientId as clientid1 from billpayment b1
      where year(b1.billdate) = 2018 and month(b1.billdate) <> 3) c
        on b.customerId = c.clientId1 
where month(b.billDate) = 3 and year(b.billDate) = 2018
and year(l.applicationDate) = 2018

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