mysql - UNION MySQL 的问题

Question

我有这个问题:

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');

我得到错误:

The used SELECT statements have a different number of columns.

我正在尝试使用 UNION 命令加入这 2 个选择，如果我们查看 returnlog_date 和 invoice_date 具有相同的数据条件，如果有任何方法可以执行将两个查询合二为一会更好。

Answer 1

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)