mysql - 选择给定年份的金额

Question

我有一张表格，其中包含国家、年份和每年的金额。我正在尝试编写一个查询，该查询将对给定年份的总金额求和并将其作为列提供给我。

例如，输出如下所示:

Country   1991     1992     1993
France     25       12       38

我试过这样的查询，但无济于事:

SELECT 
     country as "Recipient", 
     SUM(usd_amount) AS "1991" WHEN project_year = 1991,
     SUM(usd_amount) AS "1992" WHEN project_year = 1992,
     SUM(usd_amount) AS "1993" WHEN project_year = 1993

FROM tb1

GROUP BY project_year, country
order by country, project_year

有什么建议吗？谢谢!克里斯

Answer 1

试一试:

SELECT 
     country as "Recipient", 
     SUM(if(project_year = 1991, usd_amount, 0)) AS "1991",
     SUM(if(project_year = 1992, usd_amount, 0)) AS "1992",
     SUM(if(project_year = 1993, usd_amount, 0)) AS "1993",
FROM tb1
GROUP BY country
ORDER BY country

PS:按项目年份排序没有意义，因为您已经在汇总了。