MySQL UNION问题

Question

我有这个查询：

SELECT COUNT(*) AS invoice_count, IFNULL(SUM(qa_invoices.invoice_total), 0)
AS invoice_total, IFNULL(SUM(qa_invoices.invoice_discount) ,0) AS invoice_discount
FROM qa_invoices
WHERE (DATE(qa_invoices.invoice_date) BETWEEN '12/06/25' AND '12/06/25') 
AND qa_invoices.status_code IN (5, 8)

UNION 

SELECT IFNULL(SUM(qa_returns.client_credit), 0) 
FROM qa_returns 
WHERE (DATE(qa_returns.returnlog_date) BETWEEN '12/06/25' AND '12/06/25');

我收到错误：

The used SELECT statements have a different number of columns.

我正在尝试使用UNION命令将这2个选择结合在一起，如果我们看起来returnlog_date和invoice_date具有相同的数据条件，那么如果有任何方法可以将两个查询都合并为一个，那会更好。

Answer 1

该错误告诉您确切的问题是什么，对于UNION ，每个查询中的列数必须相同。

我不确定第二个查询中的哪一列与第一个查询相对应，但是您可以在第二个查询中插入零。

像这样：

SELECT COUNT(*) AS invoice_count
    , IFNULL(SUM(qa_invoices.invoice_total), 0)  AS invoice_total
    , IFNULL(SUM(qa_invoices.invoice_discount) ,0) AS invoice_discount
FROM qa_invoices 
WHERE (DATE(qa_invoices.invoice_date) BETWEEN '12/06/25' AND '12/06/25') 
    AND qa_invoices.status_code IN (5, 8)

UNION 

SELECT 0
    , IFNULL(SUM(qa_returns.client_credit), 0) 
    , 0
FROM qa_returns 
WHERE (DATE(qa_returns.returnlog_date) BETWEEN '12/06/25' AND '12/06/25');

Answer 2

使用子选择：

SELECT
    COUNT(*) AS invoice_count,
    IFNULL(SUM(invoice_total), 0) AS invoice_total,
    IFNULL(SUM(invoice_discount), 0) AS invoice_discount,
    (
        SELECT IFNULL(SUM(qa_returns.client_credit), 0)
        FROM qa_returns
        WHERE qa_returns.returnlog_date >= '2012-06-25'
        AND qa_returns.returnlog_date < '2012-06-26'
    ) AS client_credit
FROM qa_invoices
WHERE invoice_date >= '2012-06-25'
AND invoice_date < '2012-06-26'
AND status_code IN (5, 8)

Answer 3

您联合在一起的结果集必须具有完全相同的列。

Answer 4

为了做一个UNION，你需要有相同数量的列