date_part - 当使用where子句时出现错误。

Posted 2021-03-19

我有一张桌子，看起来像这样

我想把销售额加起来，只显示2010年的销售额。 使用DATE_PART可以工作，除了当我尝试使用WHERE子句时

SELECT date_part('year', date) AS year, SUM(weekly_sales) as yearly_sales
FROM sales
GROUP BY year

SELECT date_part('year', date) AS year, SUM(weekly_sales) as yearly_sales
FROM sales
GROUP BY year
WHERE year = 2010;

是不是因为date_part是双精度？

答案

该 WHERE 该条款 之前 的 GROUP BY 子句中定义的列别名，并且它不能访问在 SELECT 条款。

你可以这样做。

SELECT date_part('year', date) AS year, SUM(weekly_sales) as yearly_sales
FROM sales
WHERE date_part('year', date) = 2010
GROUP BY year

或者，更有效的。

SELECT 2010 AS year, SUM(weekly_sales) as yearly_sales
FROM sales
WHERE date >= date '2010-01-01' and date < date '2011-01-01'