Postgres - AVG计算

Question

请参考以下查询

SELECT  sum(sales) AS "Sales",
        sum(discount) AS "discount",
        year
 FROM Sales_tbl 
 WHERE Group by year

现在我还想显示一个 AVG(sales) 列，该列具有相同的值并且基于总销售额列

输出

请指教

Answer 1

将AVG()用作window函数：

WITH t AS (
  SELECT 
    SUM(sales) AS sales, SUM(discount) AS discount, year
  FROM tbl_sales
  GROUP BY year 
) 
SELECT *,AVG(sales) OVER w_total 
FROM t
WINDOW w_total AS (RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING)
ORDER BY year;

框架 RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING 在这种情况下几乎是可选的，但在 window 函数中尽可能明确被认为是一种很好的做法。所以你也可以这样写查询：

WITH t AS (
  SELECT 
    SUM(sales) AS sales, SUM(discount) AS discount, year
  FROM tbl_sales
  GROUP BY year
) 
SELECT *,AVG(sales) OVER () 
FROM t
ORDER BY year;

演示：db<>fiddle

Postgres - AVG计算

Postgres - AVG calculation

sql

postgresql

postgresql-9.5