MySQLの、どのように私はSELECTクエリ

Question

でサブクエリフィールドを参照することができ、私は次のクエリ

SELECT accountNumber, 
(
    SELECT amount 
    FROM accountDebits 
    WHERE accountNumber = accounts.accountNumber 
) debits, 
(
    SELECT amount 
    FROM accountCredits 
    WHERE accountNumber = accounts.accountNumber 
) credits, 
credits - debits as balance 
FROM accounts 

を使用してMySQLに口座残高を計算しようとしています。しかし、私はこのエラーを取得：

どう

Error Code: 1054. Unknown column 'credits' in 'field list'

selectのサブクエリ別名を参照できますか？

Answer 1

計算を行い、別のサブクエリでそれをラップ：

SELECT accountNumber, debits, credits, credits - debits as balance 
FROM (
    SELECT 
     a.accountNumber, 
     coalesce(sum(d.amount), 0) debits, 
     coalesce(sum(c.amount), 0) credits, 
    FROM accounts a 
    LEFT JOIN accountDebits d 
    ON d.accountNumber = a.accountNumber 
    LEFT JOIN accountCredits c 
    ON c.accountNumber = a.accountNumber 
) x 

Answer 2

使用インクルード：これはあなたのクエリの稼働を取得している間、あなたは外部結合を持つ方が良いと思います

SELECT accountNumber, debits, credits, credits - debits as balance 
FROM (
    SELECT accountNumber, 
    (
    SELECT amount 
    FROM accountDebits 
    WHERE accountNumber = accounts.accountNumber 
) debits, 
    (
    SELECT amount 
    FROM accountCredits 
    WHERE accountNumber = accounts.accountNumber 
) credits 
    FROM accounts 
) x 

テーブルフィールドコンベンションはうまくいくはずです

SELECT accountNumber, 
(
    SELECT amount 
    FROM accountDebits 
    WHERE accountNumber = accounts.accountNumber 
) debits, 
(
    SELECT amount 
    FROM accountCredits 
    WHERE accountNumber = accounts.accountNumber 
) credits, 
credits.amount - debits.amount as balance 
FROM accounts 

Answer 3

私はあなたがこれをしたいと思う：

SELECT a.*, 
     (COALESCE(credits, 0) - COALESCE(debits, 0)) as balance 
FROM (SELECT accountNumber, 
      (SELECT SUM(ad.amount) 
       FROM accountDebits ad 
       WHERE ad.accountNumber = a.accountNumber 
      ) as debits, 
      (SELECT SUM(ac.amount) 
       FROM accountCredits ac 
       WHERE ac.accountNumber = a.accountNumber 
      ) credits 
     FROM accounts a 
    ) a; 

同じSELECTの派生列を参照できないため、サブクエリが必要です。すべての借方/貸方を各アカウントの単一の値にまとめる集約関数が必要です。