如何在MySQL SUM子查询中创建可用别名

Question

在以下MySQL查询中，我能够生成一个Sum值，但无法分配一个可用于在PHP页面中回显的值。

SELECT
    invoices.InvoiceNo AS Invoice,
    invoices.invDate AS DATE,
    invoices.invValue AS Amount,
    (
        SELECT SUM(invoices.invValue) AS GrandTotal
        FROM invoices
        WHERE invoices.fKey = 186 AND inv_openClosed = 0
    )
FROM invoices
WHERE invoices.fKey = 186 AND inv_openClosed = 0
ORDER BY Invoice DESC

测试显示结果，但是“ GrandTotal”的别名不起作用。而且从MySQL出发寻求解决方案没有错误。

这是查询的结果：

Answer 1

别名必须位于外部查询中，而不是内部查询中：

SELECT i.InvoiceNo AS Invoice,
       i.invDate AS DATE,
       i.invValue AS Amount,
       (SELECT SUM(i2.invValue)
        FROM invoices i2
        WHERE i2.fKey = 186 AND i2.inv_openClosed = 0
       )  AS GrandTotal
FROM invoices i
WHERE i.fKey = 186 AND i.inv_openClosed = 0
ORDER BY i.Invoice DESC;

您会注意到，我还包括表别名和限定的列名。您也可以将其编写为相关子查询，因此无需重复常量：

       (SELECT SUM(i2.invValue)
        FROM invoices i2
        WHERE i2.fKey = i.fKey AND i2.inv_openClosed = i.inv_openClosed
       )  AS GrandTotal

在MySQL 8+中，您可以使用窗口函数：

SELECT i.InvoiceNo AS Invoice,
       i.invDate AS DATE,
       i.invValue AS Amount,
       SUM(i.invValue) OVER (PARTITION BY fKey, inv_openClosed) as GrandTotal
FROM invoices i
WHERE i.fKey = 186 AND i.inv_openClosed = 0
ORDER BY i.Invoice DESC;

Answer 2

在子查询中使用别名代替其结果：

SELECT
    invoices.InvoiceNo AS Invoice,
    invoices.invDate AS DATE,
    invoices.invValue AS Amount,
    (
        SELECT SUM(invoices.invValue) 
        FROM invoices
        WHERE invoices.fKey = 186 AND inv_openClosed = 0
    ) AS GrandTotal
FROM invoices
WHERE invoices.fKey = 186 AND inv_openClosed = 0
ORDER BY Invoice DESC