Question

我无法在Mysql中查看子查询。相当简单的是好的，我发现的大多数教程很少超出典型的：

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

我想从我的数据库中取出的是以下内容（我将尽力解释这个没有任何背景的数据库）：

检索属于特定代表的客户列表以及上个月（在一列中）花费的总金额以及在其他列中的当月支出金额。

结果显示，大致如下：

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

我用来获取数据的第一部分的查询如下：

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变量最终会在这里。作为一个例子，这只是给我有效的数据。

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。我一直收到#1242 - Subquery returns more than 1 row错误。

请提出任何建议或意见？

提前致谢。罗布

Answer 1

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

Answer 2

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 - 只有一个值才能被接受。

因此您需要将其更改为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)

这完全取决于您想要获得的数据。

Answer 3

我正在遗漏日期计算，因为你是从代码生成的：

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

Answer 4

OMG小马关于你为什么会遇到这个错误是正确的。在比较中使用的子查询必须始终返回单个值。

我的猜测是你需要创建两个子查询（一个用于prev，一个用于curr）并按用户ID连接它们。像这样：

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

Answer 5

我同意雅各布的观点，但提出了一种略有不同的方法：

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

不确定哪种效率更高。

无法得到mysql子查询

5 个答案: