SELECT ID，其中多列的最小值或最大值

Question

我正在寻找一个快速的MySQL查询，该查询返回与所有价格类别（ a, b, c和d ）相比价格最低（ min ）或价格最高（ max ）的产品ID 。

我有一个名为chocolate_stock的产品表，其中包含几个价格类别。 从特定类别（ a或b或c或d ）获得最低（ min ）或最高（ max ）价格是很容易的。

id |      name       | price_a | price_b | price_c | price_d |
--------------------------------------------------------------
1  |   Chips Ahoy    |   250   |   530   |   720   |   120 
--------------------------------------------------------------
2  | Chocolate Chunk |   250   |   90    |  32.92  |   110   
--------------------------------------------------------------
3  |      Oreo       |   103   |  44.52  |   250   |   850   
--------------------------------------------------------------

价格类别为decimal(10,2) 。 这是一个从类别中返回最高价格的示例， 但未返回ID：

$t = 'chocolate_stock';
$arrIds = array(1, 3);

$strQuery = "SELECT id, 
             MAX(price_a) AS price_a, 
             MAX(price_b) AS price_b, 
             MAX(price_c) AS price_c, 
             MAX(price_d) AS price_d 
             FROM $t WHERE id IN(". implode(',', array_map('intval', $arrIds)) .")";

检索此信息的最快方法是什么？

Answer 1

如果要制表一下您希望输出的外观可能会有所帮助，但是我认为您缺少的是HAVING子句。

首先-试试这个

select min(id), max(price_a) from $t having price_a = max(price_a)

然后尝试

select min(id), min(price_a) from $t having price_a = min(price_a)
union
select min(id), max(price_a) from $t having price_a = max(price_a)

Answer 2

此查询可满足您的需求：

(select t.*
 from $t t
 where . . .
 order by price_a desc
 limit 1) union all
 (select t.*
 from $t t
 where . . .
 order by price_b desc
 limit 1) union all
(select t.*
 from $t t
 where . . .
 order by price_c desc
 limit 1) union all
(select t.*
 from $t t
 where . . .
 order by price_d desc
 limit 1)

如果您在id上有一个索引，它应该会表现良好。

该方法需要遍历表四次（尽管id上的索引应大大减少该次数）。 以下方法仅需要遍历表一次：

select MAX(price_a),
       substring_index(group_concat(id order by price_a desc), ',', 1),
       max(price_b),
       substring_index(group_concat(id order by price_b desc), ',', 1),
       max(price_c),
       substring_index(group_concat(id order by price_c desc), ',', 1),
       max(price_d),
       substring_index(group_concat(id order by price_d desc), ',', 1)
from $t
where . . .

它使用一个带有group_concat()和substring_index()的技巧来获取每个列的最大id。

Answer 3

您要做的第一件事是规范化数据，为了便于以后查询，我将创建以下视图：

CREATE VIEW NormalT
AS
    SELECT  ID, Name, 'Price_a' AS Type, Price_a AS Price
    FROM    T
    UNION ALL
    SELECT  ID, Name, 'Price_b' AS Type, Price_b AS Price
    FROM    T
    UNION ALL
    SELECT  ID, Name, 'Price_c' AS Type, Price_c AS Price
    FROM    T
    UNION ALL
    SELECT  ID, Name, 'Price_d' AS Type, Price_d AS Price
    FROM    T;

然后我不确定您想要的格式，如果您想要每个价格的最小值和最大值，您可以使用以下格式：

SELECT  mt.Type2,
        mt.Type,
        mt.Price,
        t.ID,
        t.Name
FROM    (   SELECT  Type, MIN(Price) AS Price, 'MIN' AS Type2
            FROM    NormalT
            GROUP BY Type
            UNION ALL
            SELECT  Type, MAX(Price) AS Price, 'MAX' AS Type2
            FROM    NormalT
            GROUP BY Type
        ) mt
        INNER JOIN NormalT T
            ON mt.Type = T.Type
            AND mt.Price = t.Price
ORDER BY mt.Type2, mt.Type, t.ID;

它将从您的样本数据中输出以下内容：

TYPE2   TYPE        PRICE   ID  NAME
MAX     Price_a     250     1   Chips Ahoy
MAX     Price_a     250     2   Chocolate Chunk
MAX     Price_b     530     1   Chips Ahoy
MAX     Price_c     720     1   Chips Ahoy
MAX     Price_d     850     3   Oreo
MIN     Price_a     103     3   Oreo
MIN     Price_b     44.52   3   Oreo
MIN     Price_c     32.92   2   Chocolate Chunk
MIN     Price_d     110     2   Chocolate Chunk

但是，如果它只是所有价格（a，b，c和d）的最小值和最大值，则可以使用以下方法：

SELECT  mt.Type2,
        t.Type,
        mt.Price,
        t.ID,
        t.Name
FROM    (   SELECT  MIN(Price) AS Price, 'MIN' AS Type2
            FROM    NormalT
            UNION ALL
            SELECT  MAX(Price) AS Price, 'MAX' AS Type2
            FROM    NormalT
        ) mt
        INNER JOIN NormalT T
            ON mt.Price = t.Price;

将输出以下内容：

TYPE2   TYPE    PRICE       ID  NAME
MIN     Price_c     32.92   2   Chocolate Chunk
MAX     Price_d     850     3   Oreo

SQL小提琴上的示例

Answer 4

试试看，它模拟Analytics（分析），因为默认情况下MYSQL没有它们：

SELECT id, 
             ( select MAX(price_a) from $t t2 where  t2.id = t1.id ) AS price_a, 
             ( select MAX(price_b) from $t t2 where  t2.id = t1.id ) AS price_b, 
             ( select MAX(price_c) from $t t2 where  t2.id = t1.id ) AS price_c, 
             ( select MAX(price_d) from $t t2 where  t2.id = t1.id ) AS price_d 
             FROM $t t1 WHERE id IN(". implode(',', array_map('intval', $arrIds)) .")

资料来源： http : //www.oreillynet.com/pub/a/mysql/2007/03/29/emulating-analytic-aka-ranking-functions-with-mysql.html?page=3

Answer 5

您没有得到id，因为MAX返回一个值。 但是id并非如此。您可以使用单独的查询，例如

SELECT id,MAX(price_a) FROM $t WHERE id IN (". implode(',', array_map('intval', $arrIds)).")";
SELECT id,MAX(price_b) FROM $t WHERE id IN (". implode(',', array_map('intval', $arrIds)).")";

等等