如何在新列中输出每年的结果？

Question

此代码在一行中显示数据，但我需要在单独的列中显示每年的结果。你能帮帮我吗？

SELECT 
EXTRACT (YEAR FROM s.time_id)::int,
p.prod_subcategory,
sum(s.amount_sold)
FROM sales s
JOIN products p ON p.prod_id = s.prod_id
WHERE EXTRACT (YEAR FROM s.time_id) IN (1998,1999,2001)
GROUP BY EXTRACT (YEAR FROM s.time_id)::int, p.prod_subcategory
ORDER BY date_part;

Answer 1

使用条件聚合：

SELECT p.prod_subcategory,
       SUM(s.amount_sold) FILTER (WHERE EXTRACT(YEAR FROM s.time_id) = 2000) as sales_2000,
       SUM(s.amount_sold) FILTER (WHERE EXTRACT(YEAR FROM s.time_id) = 1999) as sales_1999,
       SUM(s.amount_sold) FILTER (WHERE EXTRACT(YEAR FROM s.time_id) = 1998) as sales_1998
FROM sales s JOIN
     products p
     ON p.prod_id = s.prod_id
WHERE EXTRACT (YEAR FROM s.time_id) IN (1998,1999,2001)
GROUP BY p.prod_subcategory;

Answer 2

简单但不灵活的hard-coded方式——使用过滤器子句：

SELECT
  p.prod_subcategory,
  sum(s.amount_sold) filter (where EXTRACT(YEAR FROM s.time_id)::int = 1998) as amount_1998,
  sum(s.amount_sold) filter (where EXTRACT(YEAR FROM s.time_id)::int = 1999) as amount_1999,
  sum(s.amount_sold) filter (where EXTRACT(YEAR FROM s.time_id)::int = 2001) as amount_2001
FROM sales s
JOIN products p ON p.prod_id = s.prod_id
WHERE EXTRACT(YEAR FROM s.time_id) IN (1998,1999,2001)
GROUP BY p.prod_subcategory
ORDER BY _whatever-you-need_;

一种更通用、更优雅的方法是使用扩展 tablefunc、函数 crosstab。这是一个 SO thread 。

如何在新列中输出每年的结果？

How to output results for each year in a new column?

sql

postgresql

subquery