Question

这是一个常见的SQL问题，但我必须知道数据库是Firebird。

我有这张桌子（简化）：

user  amount  type
--------------------
john  25      credit
john  20      debit
john  5       debit
john  15      credit
mike  15      credit

我希望使用单个查询得到一个如下所示的结果：

user  credit  debit
--------------------
john  40      25
mike  15      NULL

Where credit = SUM(amount) WHERE type=credit
   and debit = SUM(amount) WHERE type=debit

基本上我希望基于字段的SUM（在这种情况下是数量）在结果上有多个字段，但是在不同的条件下（在这种情况下是类型）。

提前感谢任何建议。

Answer 1

标准SQL将是：

SELECT "user",
    SUM(CASE WHEN type='credit' then amount END) as Credit,
    SUM(CASE WHEN type='debit' then amount END) as Debit
FROM
    "table"
GROUP BY
    "user"

Answer 2

我不确定Firebird是如何做到的，但你可以这样做：

SELECT user, 
sum(SELECT amount FROM table AS t2 WHERE t2.user = t1.user AND type="credit" ) AS credit, 
sum(SELECT amount FROM table AS t3 WHERE t3.user = t1.user AND type="debit" ) AS debit
FROM table AS t1
GROUP BY user
ORDER BY user

我正在引用PostgreSQL中我认为的内容，以防止您找到所需内容。

Answer 3

试试这个：

SELECT credit.user_name, credit.cre, debit.deb
  FROM (SELECT user_name, SUM(amount) cre FROM t WHERE TYPE = 'credit' GROUP BY user_name) credit
  LEFT OUTER JOIN (SELECT user_name, SUM(amount) deb
                     FROM t
                    WHERE TYPE = 'debit'
                    GROUP BY user_name) debit
    ON (credit.user_name = debit.user_name)

SQL - 每列的条件

3 个答案: