SQL計算交易余額

Question

用戶表：

| user_id | user_name | credit |
| ------- | --------- | ------ |
| 1       | Winston   | 100    |
| 2       | Moustafa  | 600    |
| 3       | Jonathan  | 800    |
| 4       | Maria     | 100    |

交易表：

| trans_id | paid_by | paid_to | amount | transacted_on |
| -------- | ------- | ------- | ------ | ------------- |
| 1        | 2       | 4       | 1000   | 2020-08-28    |
| 2        | 3       | 2       | 600    | 2020-08-06    |
| 3        | 2       | 4       | 800    | 2020-08-15    |
| 4        | 1       | 3       | 800    | 2020-09-02    |
| 5        | 3       | 4       | 100    | 2020-08-02    |
| 6        | 3       | 4       | 500    | 2020-08-08    |
| 7        | 3       | 4       | 800    | 2020-09-17    |

我的代碼：

WITH tb1 AS (SELECT u.user_id, u.user_name, u.credit AS initial_amount,
SUM(t1.amount) AS credit_out, SUM(t2.amount) AS credit_in
FROM Users u
LEFT JOIN Transactions t1
ON u.user_id = t1.paid_by
LEFT JOIN Transactions t2
ON u.user_id = t2.paid_to
GROUP BY u.user_id),
tb2 AS (SELECT user_id, user_name, 
(initial_amount - IFNULL(credit_out,0) + IFNULL(credit_in,0)) AS credit
FROM tb1)
SELECT user_id,user_name,credit,
CASE WHEN credit < 0 THEN 'Yes' ELSE 'No' END AS credit_limit_breached
FROM tb2

我的想法是首先根據paid_by和paid_to將Transaction表加入到Users中，並計算這些交易過程中的進出信用。 然后將 initial_amount、credit_in 和 credit_out 相加以獲得用戶帳戶中的最終信用。

我的輸出是：

| user_id | user_name | credit | credit_limit_breached |
| ------- | --------- | ------ | --------------------- |
| 1       | Winston   | -700   | Yes                   |
| 2       | Moustafa  | 0      | No                    |
| 3       | Jonathan  | 2000   | No                    |
| 4       | Maria     | 3300   | No                    |

預期的輸出是：

| user_id | user_name | credit | credit_limit_breached |
| ------- | --------- | ------ | --------------------- |
| 2       | Moustafa  | -600   | Yes                   |
| 3       | Jonathan  | -400   | Yes                   |
| 1       | Winston   | -700   | Yes                   |
| 4       | Maria     | 3300   | No                    |

我無法弄清楚我的代碼的哪一步是錯誤的，為什么我得到這些信用計算......

Answer 1

問題是關於join 。 如果分解第一個 CTE 查詢：

SELECT u.user_id, u.user_name, u.credit AS initial_amount, t1.amount AS credit_out, t2.amount AS credit_in
FROM Users u
    LEFT JOIN Transactions t1
        ON u.user_id = t1.paid_by
    LEFT JOIN Transactions t2
        ON u.user_id = t2.paid_to

WHERE u.user_id = 2

您在這里沒有得到一行，您得到的是具有重復值的 t1 x t2 行。 這就是提供不正確的SUM結果的 beeing 聚合。 嘗試一個沒有 CTE 或額外連接的更簡單的查詢：

SELECT 
    overall.user_id, 
    Users.user_name,
    SUM(overall.amount) as balance,
    IF( SUM(overall.amount) < 0 , "Yes", "No") as credit_limit_breached
FROM(

    SELECT outbount.paid_by as user_id, SUM(outbount.amount) * -1 as amount
            FROM Transactions outbount
        GROUP BY paid_by
    UNION ALL
        SELECT inbound.paid_to as user_id, SUM(inbound.amount) as amount 
            FROM Transactions inbound
        GROUP BY paid_to
    UNION ALL
        SELECT initial.user_id as user_id, initial.credit as amount 
            FROM Users initial

) overall
LEFT JOIN Users
    ON overall.user_id = Users.user_id
GROUP BY user_id