MySQL 应该使用哪个查询语句？

Question

我有一个如下所示的数据集，例如第 1 行，对价格为 3 美元的商品进行了 0 次购买，对价格为 30 美元的商品进行了 3 次购买。 我需要编写一个查询，通过将价格分类为“0-10”、“11-20”、“21-30”、“31-40”的价格范围来提供购买了多少通行证的摘要。 我假设应该何时使用案例，但我不确定如何使用。 请帮忙。

+-----------------+-----------------+--------------------------+--------------------------+
| price_category1 | price_category2 | purchase_count_category1 | purchase_count_category2 |
+-----------------+-----------------+--------------------------+--------------------------+
|               3 |              30 |                        0 |                        3 |
|              20 |               6 |                        1 |                        4 |
|              25 |              11 |                        4 |                        0 |
|              17 |              12 |                        0 |                        1 |
+-----------------+-----------------+--------------------------+--------------------------+

+------+-------+-------+-------+
| 0-10 | 11-20 | 21-30 | 31-40 |
+------+-------+-------+-------+
|    4 |     2 |     7 |     0 |
+------+-------+-------+-------+

Answer 1

你可以试试下面。

工作解决方案

WITH MAIN
     AS (SELECT 3 AS price_category1,
                30 AS price_category2,
                0 purchase_count_category1,
                3 AS purchase_count_category2
           FROM DUAL
         UNION ALL
         SELECT 20 AS price_category1,
                6 AS price_category2,
                1 purchase_count_category1,
                4 AS purchase_count_category2
           FROM DUAL
         UNION ALL
         SELECT 25 AS price_category1,
                11 AS price_category2,
                4 purchase_count_category1,
                0 AS purchase_count_category2
           FROM DUAL
         UNION ALL
         SELECT 17 AS price_category1,
                12 AS price_category2,
                0 purchase_count_category1,
                1 AS purchase_count_category2
           FROM DUAL),
     M2
     AS (SELECT price_category1 CAT, purchase_count_category1 CNT FROM MAIN
         UNION
         SELECT price_category2, purchase_count_category2 FROM MAIN)
  SELECT CASE
            WHEN CAT >= 0 AND CAT < 11 THEN '0-10'
            WHEN CAT >= 11 AND CAT < 21 THEN '11-20'
            WHEN CAT >= 21 AND CAT < 31 THEN '21-30'
         END
            CAT,
         SUM (CNT) SUMM
    FROM M2
GROUP BY CASE
            WHEN CAT >= 0 AND CAT < 11 THEN '0-10'
            WHEN CAT >= 11 AND CAT < 21 THEN '11-20'
            WHEN CAT >= 21 AND CAT < 31 THEN '21-30'
         END

Answer 2

SELECT SUM(CASE WHEN price_category1 BETWEEN 0 AND 10 
                THEN purchase_count_category1 
                END) + SUM(CASE WHEN price_category2 BETWEEN 0 AND 10  
                                THEN purchase_count_category2 
                                END) AS `0-10`,
       SUM(CASE WHEN price_category1 BETWEEN 11 AND 20
                THEN purchase_count_category1 
                END) + SUM(CASE WHEN price_category2 BETWEEN 11 AND 20
                                THEN purchase_count_category2 
                                END) AS `11-20`,
       SUM(CASE WHEN price_category1 BETWEEN 21 AND 30 
                THEN purchase_count_category1 
                END) + SUM(CASE WHEN price_category2 BETWEEN 21 AND 30
                                THEN purchase_count_category2 
                                END) AS `21-30`
FROM source_table

或者

SELECT SUM(CASE WHEN cat BETWEEN 0 AND 10 
                THEN cnt
                END )  AS `0-10`,
       SUM(CASE WHEN cat BETWEEN 11 AND 20
                THEN cnt
                END )  AS `11-20`,
       SUM(CASE WHEN cat BETWEEN 21 AND 30 
                THEN cnt
                END )  AS `21-30`
FROM ( SELECT price_category1 cat, purchase_count_category1 cnt
       FROM source_table
       UNION ALL
       SELECT price_category2, purchase_count_category2
       FROM source_table ) src

PS。 该解决方案提供“水平” output - 一行包含所有需要的统计信息。 如果您需要“垂直” output 则使用ismetguzelgun提供的解决方案。

请注意 - 我的解决方案不可扩展（如果您需要更改范围数量或边界，则必须更改查询文本），而在将硬编码范围边界转换为根据 CTE 或（最好的）附加标准表后，可以轻松扩展替代解决方案。