sql - 选择总和和内连接

Question

我有两张 table

Bills :id amount reference

Transactions :id reference amount

以下 SQL 查询

SELECT 
   *,
   (SELECT SUM(amount) 
    FROM transactions 
    WHERE transactions.reference = bils.reference) AS paid
FROM bills
GROUP BY id HAVING paid<amount

原意是表 Bills 中的某些行, 添加一列 paid与关联交易金额之和。

但是，它仅在每张账单至少有一笔交易时才有效。否则，不返回无交易账单的行。

可能，那是因为我应该做一个内部连接!

所以我尝试以下操作:

SELECT 
   *,
   (SELECT SUM(transactions.amount) 
    FROM transactions 
    INNER JOIN bills ON transactions.reference = bills.reference) AS paid
FROM bills
GROUP BY id 
HAVING paid < amount

但是，这会为所有行返回相同的paid 值!我究竟做错了什么 ？

Answer 1

使用左连接而不是子查询:

select b.id, b.amount, b.paid, sum(t.amount) as transactionamount
from bills b
left join transactions t on t.reference = b.reference
group by b.id, b.amount, b.paid
having b.paid < b.amount

编辑:
要将交易总和与金额进行比较，请处理没有交易时获得的空值:

having isnull(sum(t.amount), 0) < b.amount