我有以下数据库表,我希望能够计算每个销售人员的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的结果集;
|------------|-------------|------------|------------|------------|
|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,因为对于每个括号中的SELECT,user_id与主SELECT语句中的外部user_id不匹配。
有人可以帮帮我吗?
谢谢你
答案 0 :(得分:82)
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
答案 1 :(得分:18)
您正在尝试转动数据。 MySQL没有pivot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;
答案 2 :(得分:3)
看看是否有效:
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:可能会有更好的方法来达到相同的结果。