MySQL的倍數SUM（）一個查詢的領域內功能

Question

我試圖讓每個以下款項的領域，我只得到了一個外，其他兩個返回undefined指數。

我怎麼把它們作爲外場？

SELECT 
(SELECT SUM(amount) AS income 
    FROM transaction 
    WHERE 
    type = '1' && state = 'a') 

- (SELECT SUM(amount) AS expense 
    FROM transaction 
    WHERE 
    type = '2' && state = 'a') 
    AS balance 

平衡工程，但收入和費用我得到未定義的指數。

Answer 1

使用條件彙總：

SELECT SUM(CASE WHEN type = '1' AND state = 'a' THEN amount ELSE 0 
      END) as income, 
     SUM(CASE WHEN type = '2' AND state = 'a' THEN amount ELSE 0 
      END) as balance 
FROM transaction; 

如果你仍然想的區別，那麼你需要重複的邏輯：

SELECT SUM(CASE WHEN type = '1' AND state = 'a' THEN amount ELSE 0 
      END) as income, 
     SUM(CASE WHEN type = '2' AND state = 'a' THEN amount ELSE 0 
      END) as expense, 
     (SUM(CASE WHEN type = '1' AND state = 'a' THEN amount ELSE 0 END) - 
     SUM(CASE WHEN type = '2' AND state = 'a' THEN amount ELSE 0 END) 
     ) as balance 
FROM transaction; 

編輯：

其實，這是最好的共同條件分解出爲WHERE條款：

SELECT SUM(CASE WHEN type = '1' THEN amount ELSE 0 END) as income, 
     SUM(CASE WHEN type = '2' THEN amount ELSE 0 END) as expense, 
     (SUM(CASE WHEN type = '1' THEN amount ELSE 0 END) - 
     SUM(CASE WHEN type = '2' THEN amount ELSE 0 END) 
     ) as balance 
FROM transaction 
WHERE state = 'a' AND type IN ('1', '2'); 

這可以在transaction(state, type, amount)採取指數的優勢。

Answer 2

您可以使用case和sum讓每一個結果：

select sum(case when `type` = '1' then `amount` else 0 end) as `income` 
    , sum(case when `type` = '2' then `amount` else 0 end) as `expense ` 
    , sum((case when `type` = '2' then -1 else 1 end) * `amount`) as `difference` 
from `transaction` 
where `type` in ('1', '2') 
where `state` = 'a' 

Answer 3

您不能訪問income和expense，因爲它們只在其各自的子查詢中定義，而不在頂級查詢中定義，而頂級查詢只有一個字段 - 它們之間的差異。我把一個子查詢，然後選擇他們兩個和他們之間的差異。爲了使這個查詢更方便，刪除子查詢的需要，您可以通過在sum的參數提取不同的條件case表情模擬兩種不同where條款的行爲：

SELECT income, expense, income - expense AS balance 
FROM (SELECT SUM(CASE type WHEN 1 THEN amount ELSE NULL) AS income, 
       SUM(CASE type WHEN 2 THEN amount ELSE NULL) AS expense, 
     FROM `transaction` 
     WHERE state = 'a') t