總和案例當查詢

Question

這是一般的SQL問題

我有這個表（簡體），信用是積極的，借方是負值：

Account Amount Type 
-------------------- 
john 25  credit 
john 45  debit 
john 5  debit 
john 15  credit 
mike 15  credit 

我想有一個結果，看起來像這樣，使用單個查詢使用Case When：

Account Total 
-------------------- 
john  -10  
mike  15  

在此先感謝您的任何建議。

Answer 1

您可以使用CASE構造來區分借記和貸記條目。

SELECT account, SUM (amount * CASE type WHEN 'credit' THEN 1 ELSE -1 END) 
FROM  my_table 
GROUP BY account 

Answer 2

sum(amount * case when type = 'debit' then -1 else 1 end) 

Answer 3

您也可以嘗試，如果它更有意義給你以下幾點：

SELECT a.Account, b.Credits - a.Debits AS Total FROM 
    (SELECT Account, SUM(Amount) AS Debits 
     FROM YourTable GROUP BY Account HAVING Type = 'debit' 
    ) AS a 
    INNER JOIN 
    (SELECT Account, SUM(Amount) AS Credits 
     FROM YourTable GROUP BY Account HAVING Type = 'credit' 
    ) AS b