MySQL 条件分组？

Question

我有 SQL 代码 returns 客户的总余额 id:35

SELECT
    d.customer_id,
    SUM( IF(d.side="K" AND d.type<>"employee-cash-out", -ABS(d.total), ABS(d.total)) ) AS total,
    d.currency_id
FROM dea_documents d
WHERE d.customer_id=35 OR d.parent_customer_id=35
GROUP BY d.currency_id
ORDER BY d.customer_id, d.document_date

示例结果：

customer_id | total       | currency_id
35          | 8.08        | USD
35          | 1.52        | EUR

问题是文档必须按（d.customer_id 或 d.parent_customer_id）分组。

是否可以对所有分组的客户进行 SELECT？:

customer_id | total       | currency_id
13          | 139749.54   | USD
13          | 4283.62     | EUR
17          | 60.00       | USD
17          | -11.57      | EUR
29          | 13498.67    | USD
29          | -347.29     | EUR

更新：

我得到了这段代码

SELECT
    d2.customer_id, 
    SUM( d2.amount ) AS total,
    d2.currency_id
FROM
    (
        SELECT
            IF(parent_customer_id<>"", parent_customer_id, customer_id) AS customer_id,
            currency_id,
            IF(d.side="K" AND d.type<>"employee-cash-out", -ABS(d.total), ABS(d.total)) AS amount
        FROM dea_documents d
    ) d2
GROUP BY d2.customer_id, d2.currency_id
ORDER BY total DESC

标记为 Barmar 的答案，因为它对我有帮助，而且是最接近的答案:)

Answer 1

在分组之前使用 UNION 将 customer_id 和 parent_customer_id 放入同一列：

SELECT d.customer_id, 
        SUM( IF(d.side="K" AND d.type<>"employee-cash-out", -ABS(d.total), ABS(d.total)) ) AS total,
        d.currency_id
FROM (
    SELECT customer_id, side, total, currency_id
    FROM dea_documents
    UNION
    SELECT parent_customer_id as customer_id, side, total, currency_id
    FROM dea_documents) AS d
GROUP BY d.customer_id, d.currency_id
ORDER BY d.customer_id, d.currency_id

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