无法绕过mysql子查询答案

【问题标题】：Can't get head round mysql subquery无法绕过mysql子查询
【发布时间】：2011-03-30 12:45:58
【问题描述】：

我无法在 Mysql 中处理子查询。相当简单的也可以，而且我发现的大多数教程很少超出典型：

SELECT * FROM t1 WHERE column1 = (SELECT column1 FROM t2);

我试图从我的数据库中提取的内容如下（我会尽力解释这一点，而无需任何数据库背景）：

在另一列中检索属于特定代表的客户列表和上个月花费的总金额（在一个列中）和本月迄今花费的金额。

结果大致如下：

ID | NAME   | PREV MONTH | CUR MONTH
1  | foobar | £2300      | £1200
2  | barfoo | £1240      | £500

我用来获取第一部分数据的查询如下：

SELECT c.id,c.name, SUM(co.invoicetotal) as total
FROM customers as c
JOIN customerorders as co on co.customer_id = c.id
WHERE c.salesrep_id = 24
AND co.orderdate BETWEEN DATE_SUB(CURDATE(), INTERVAL 30 DAY) AND CURDATE()
GROUP by c.id
order by total desc

DATE_SUB 可以替换为实际日期，因为 php 变量最终会出现在这里。作为一个例子，这只是给了我有效的数据。

这给了我，例如：

ID | NAME   | TOTAL 
1  | foobar | £2300      
2  | barfoo | £1240

因此，理想情况下，我的子查询将是完全相同的查询，但日期已更改。我不断收到#1242 - Subquery returns more than 1 row 错误。

请问有什么建议或意见吗？

提前致谢。抢

【问题讨论】：

标签： sql mysql subquery mysql-error-1242

【解决方案1】：

您收到错误的原因是：

WHERE column1 = (SELECT column1 FROM t2)

t2.column1 正在返回多个结果，但由于子查询之前的等号运算符 - 只能接受一个值.

所以您要么需要将其更改为 IN：

WHERE column1 IN (SELECT column1 FROM t2)

...接受多个值。或者将子查询更改为仅返回一个变量 - 此示例返回整个表的最高 t2.column1 值：

WHERE column1 = (SELECT MAX(column1) FROM t2)

这完全取决于您要获取的数据。

【讨论】：

【解决方案2】：

SELECT  c.id, c.name,
        (
        SELECT  SUM(co.invoicetotal)
        FROM    customerorders co
        WHERE   co.customer_id = c.id
                AND co.orderdate BETWEEN DATE_SUB(CURDATE(), INTERVAL 30 DAY) AND CURDATE()
        ) AS prev_month,
        (
        SELECT  SUM(co.invoicetotal)
        FROM    customerorders co
        WHERE   co.customer_id = c.id
                AND co.orderdate BETWEEN CURDATE() AND CURDATE() + INTERVAL 1 MONTHS
        ) AS cur_month,
FROM    customers as c
WHERE   c.salesrep_id = 24
ORDER BY
        prev_month DESC

【讨论】：

这很有效，非常感谢。也感谢其他所有人的贡献。尽管我很可能会使用 Quassnoi 的查询来满足我的目的，但我仍然会仔细阅读您的所有答案来帮助我学习，干杯。

【解决方案3】：

OMG Ponies 对您出现该错误的原因是正确的。用于比较的子查询必须始终返回单个值。

我的猜测是您需要创建两个子查询（一个用于 prev，一个用于 curr）并通过用户 ID 加入它们。像这样的：

SELECT prev.id,prev.name, prev.total, curr.total
FROM
(
SELECT c.id,c.name, SUM(co.invoicetotal) as total  
FROM customers as c JOIN customerorders as co on co.customer_id = c.id  
WHERE c.salesrep_id = 24  
AND co.orderdate BETWEEN DATE_SUB(CURDATE(), INTERVAL 30 DAY) AND CURDATE()  
GROUP by c.id ORDER BY total desc  
) as prev
JOIN
(
SELECT c.id,c.name, SUM(co.invoicetotal) as total  
FROM customers as c JOIN customerorders as co on co.customer_id = c.id  
WHERE c.salesrep_id = 24  
AND co.orderdate > CURDATE()
GROUP by c.id ORDER BY total desc  
) as curr
ON prev.id=curr.id

【讨论】：

【解决方案4】：

我省略了日期计算，因为您是从代码生成的：

SELECT c.id,c.name, 
    SUM(case when co.orderdate >= @LastMonthStartDate and co.orderdate < @CurrentMonthStartDate then co.invoicetotal else 0 end) as LastMonthTotal,
    SUM(case when co.orderdate between @CurrentMonthStartDate and CURDATE() then co.invoicetotal else 0 end) as CurrentMonthTotalToDate
FROM customers as c 
JOIN customerorders as co on co.customer_id = c.id 
WHERE c.salesrep_id = 24 
   AND co.orderdate BETWEEN @LastMonthStartDate AND CURDATE() --remove this if you want customers that did not order in the last 2 months
GROUP by c.id 
order by total desc

【讨论】：

【解决方案5】：

我同意 JacobM 的观点，但提出了一种稍微不同的方法：

SELECT
    c.id,
    c.name, 
    SUM(co1.invoicetotal) as PREV_MONTH, 
    SUM(co2.invoicetotal) as CUR_MONTH, 
FROM
    customers as c, 
    customerorders as co1, 
    customerorders as co2
WHERE 
    c.salesrep_id = 24
    and  co1.customer_id = c.id
    and  co2.customer_id = c.id
    AND co1.orderdate BETWEEN DATE_SUB(CURDATE(), INTERVAL 30 DAY) AND CURDATE()
    AND co2.orderdate > DATE_SUB(CURDATE(), INTERVAL 30 DAY)
GROUP by c.id
order by total desc

不确定哪个更有效。

【讨论】：