47

我有以下数据库表，我希望能够计算每个销售人员某些产品的销售实例。

|------------|------------|------------|
|id          |user_id     |product_id  |
|------------|------------|------------|
|1           |1           |2           |
|2           |1           |4           |
|3           |1           |2           |
|4           |2           |1           |
|------------|------------|------------|

我希望能够创建如下结果集；

|------------|-------------|------------|------------|------------|
|user_id     |prod_1_count |prod_2_count|prod_3_count|prod_4_count|
|------------|-------------|------------|------------|------------|
|1           |0            |2           |0           |1           |
|2           |1            |0           |0           |0           |
|------------|-------------|------------|------------|------------|

我正在使用这些数据创建图表，并且再次（如今天早些时候）我无法计算列总数。我试过了;

SELECT user_id, 
(SELECT count(product_id) FROM sales WHERE product_id = 1) AS prod_1_count,
(SELECT count(product_id) FROM sales WHERE product_id = 2) AS prod_2_count,
(SELECT count(product_id) FROM sales WHERE product_id = 3) AS prod_3_count,
(SELECT count(product_id) FROM sales WHERE product_id = 4) AS prod_4_count 
FROM sales GROUP BY user_id;

我可以看到为什么这不起作用，因为对于每个带括号的 SELECT，user_id 与主 SELECT 语句中的外部 user_id 不匹配。

4

3 回答 3

100

您可以使用SUMand执行此操作CASE：

select user_id,
  sum(case when product_id = 1 then 1 else 0 end) as prod_1_count,
  sum(case when product_id = 2 then 1 else 0 end) as prod_2_count,
  sum(case when product_id = 3 then 1 else 0 end) as prod_3_count,
  sum(case when product_id = 4 then 1 else 0 end) as prod_4_count
from your_table
group by user_id
于 2013-04-04T15:12:22.130 回答
28

您正在尝试旋转数据。MySQL 没有枢轴函数，因此您必须使用带有CASE表达式的聚合函数：

select user_id,
  count(case when product_id = 1 then product_id end) as prod_1_count,
  count(case when product_id = 2 then product_id end) as prod_2_count,
  count(case when product_id = 3 then product_id end) as prod_3_count,
  count(case when product_id = 4 then product_id end) as prod_4_count
from sales
group by user_id;

请参阅带有演示的 SQL Fiddle

于 2013-04-04T15:15:38.487 回答
3

看看这是否有效：

SELECT a.user_id, 
(SELECT count(b.product_id) FROM sales b WHERE b.product_id = 1 AND a.user_id = b.user_id) AS prod_1_count,
(SELECT count(b.product_id) FROM sales b WHERE b.product_id = 2 AND a.user_id = b.user_id) AS prod_2_count,
(SELECT count(b.product_id) FROM sales b WHERE b.product_id = 3 AND a.user_id = b.user_id) AS prod_3_count,
(SELECT count(b.product_id) FROM sales b WHERE b.product_id = 4 AND a.user_id = b.user_id) AS prod_4_count 
FROM sales a GROUP BY a.user_id;

干杯。注意可能有更好的方法来实现等效的结果。

于 2013-04-04T15:11:51.030 回答