SQL-每列的條件

Question

這是一個通用的SQL問題，但是我是否必須知道數據庫是Firebird。

我有這張桌子（簡體）：

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

我希望使用單個查詢獲得如下所示的結果：

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，我想基於一個字段的總和（在這種情況下為金額），但基於不同的條件（在這種情況下為類型），在結果上具有多個字段。

在此先感謝您的任何建議。

Answer 1

標准SQL將是：

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

我不確定Firebird是如何做到的，但是您可以執行以下操作：

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

我指的是PostgreSQL中可能會出現的情況，以幫助您找到所需的內容。

Answer 3

嘗試這個 ：

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)