如何在MySQL中使用ORDER BY使用变量SET

Question

此查询计算总和p_quantity <= 21000为p_description。查询工作，但是当你添加ORDER BY p_reference显示所有行

我尝试添加ORDER BY这样的：

SET @runtot:=0; 
SELECT p_id, p_description, (@runtot := @runtot + p_quantity) AS runningTotal 
FROM product_table 
WHERE @runtot + p_quantity <= 21000 AND p_description = 'product_1' ORDER BY p_reference ASC 

这是创建产品表代码：

CREATE TABLE IF NOT EXISTS `product_table` (
    `p_id` int(11) PRIMARY KEY AUTO_INCREMENT NOT NULL, 
    `p_description` varchar(50) NOT NULL, 
    `p_reference` varchar(25) NOT NULL, 
    `p_location` varchar(25) NOT NULL, 
    `p_quantity` int(11) NOT NULL 
) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=1 ; 

INSERT INTO `product_table` (`p_id`, `p_description`, `p_reference`, `p_location`, `p_quantity`) VALUES 
    (1, 'Product_1', '1A00001', 'AP07', 7000), 
    (2, 'Product_1', '1A00001', 'AF05', 6000), 
    (3, 'Product_1', '1A00233', 'DS07', 7000), 
    (4, 'Product_1', '1A00233', 'SD10', 5000), 
    (5, 'Product_1', '1A00001', 'YB12', 7000), 
    (6, 'Product_1', '1A00001', 'AN01', 7000), 
    (7, 'Product_1', '1A00001', 'AP04', 7000), 
    (8, 'Product_1', '1A00245', 'AP01', 7000), 
    (9, 'Product_1', '1A00001', 'QD01', 7000), 
    (10, 'Product_1', '1A00001', 'SC01', 7000); 

Answer 1

因为你没” t在查询中选择p_reference。尝试，

SET @runtot:=0; 
SELECT p_id, p_description, **p_reference**, (@runtot := @runtot + p_quantity) AS runningTotal 
FROM product_table 
WHERE @runtot + p_quantity <= 21000 AND p_description = 'product_1' 
ORDER BY p_reference ASC; 

Answer 2

我尝试这样的查询，但显示的所有行和p_quantity > 21000：

SELECT p_id, p_description, p_reference, (@runtot := @runtot + p_quantity) AS runningTotal 
FROM product_table 
WHERE @runtot + p_quantity <= 21000 AND p_description = 'product_1' 
ORDER BY p_reference ASC; 

这个查询而不ORDER BY显示p_quantity <=21000：

SELECT p_id, p_description, p_reference, (@runtot := @runtot + p_quantity) AS runningTotal 
FROM product_table 
WHERE @runtot + p_quantity <= 21000 AND p_description = 'product_1'; 

Answer 3

好吧，这个问题是不是更难了什么看起来像。事实上，我正在投票提出你的问题张贴这个问题:)

这里的问题是什么时候订购你的数据和什么时候应用你的数学。

想一想吧。您在p_quantity值加起来以前p_quantity值

因此，如果我们有这样

Preference Quantity 
D   7000 
B   6000 
C   7000 
A   1500 

7000 is <= 2100 so Row D is selected 
7000 + 6000 = 13000 is <= than 21000 so Row B is selected 
13000 + 7000 = 20000 is <= 21000 so Row C is selected 
20000 + 1500 = 21500 is > 210000 Row A is NOT selected and no other rows will be selected 

列表的最后行会

Preference Quantity 
D   7000 
B   6000 
C   7000 

但是，如果我们通过分类列表Preference列先做，然后做相同的数学

Preference Quantity 
A   1500 
B   6000 
C   7000 
D   7000 

1500 is <= 21000 so row A is selected 
1500 + 6000 = 7500 is <= 21000 row B is selected 
7500 + 7000 = 14500 is <= 21000 row C is selected 
14500 + 7000 = 21500 is > 21000 row D is not selected and nothing after will be selected 

最终的名单将

Preference Quantity 
A   1500 
B   6000 
C   7000 

这里的想法是，最终的结果集是怎么回事，当你做你的数学要根据各行的位置不同。

它得到解决你的问题，首先要对列表进行排序，然后运行你的数学:)

下面的查询应该解决您的问题，给你，你正在寻找

SET @runtot=0; 
-- second go through the sorted set and run your math 
SELECT p_reference, p_id, p_description, (@runtot := @runtot + p_quantity) AS runningTotal 
FROM (
    -- First generate a sorted data set 
    SELECT p_reference, p_id, p_description, p_quantity 
    FROM product_table 
    WHERE p_description = 'product_1' AND p_quantity <= 21000 
    ORDER BY p_reference 
) AS l 
WHERE @runtot + p_quantity <= 21000; 

数据集