MySQL条件分组？

我有SQL代码，返回客户id为35的总余额

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

问题是文档必须按d.customer\u id或d.parent\u customer\u id进行分组

是否可以对所有分组的客户进行选择

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：

我最终得到了这个密码

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Barmar回答，因为它在这里帮助了我，而且是最接近的一个：

在分组之前，使用联合将客户id和父客户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

---

是否应将每个文档同时添加到其自己的客户ID和其父客户ID？是否有任何原因使您无法按d.customer\u ID、d.currency\u ID进行分组？@Tim文档必须按[d.customer\u ID或d.parent\u customer\u ID]进行分组。你读过这个问题吗？@Barmar它不是必需的。如果它不是同时在两个组中，你如何确定它应该在哪个组中？这看起来是一个很好的解决方案！目前它正在返回奇怪的数量。。。我将对它进行更多的测试。如果您发布原始表数据和期望的结果，我可以尝试找出它产生奇怪结果的原因。也许你应该回答我在上面评论中提出的问题，这可能是相关的。他现在情绪低落。我将上传一些数据时，它是可访问的。

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