选择给定年份的金额

Question

我有一张表，每年的国家，年份和金额。我试图编写一个查询，将总和给定年份的总金额，并将其作为列给我。

例如，有一个输出，看起来像：

Country 1991  1992  1993 
France  25  12  38 

我想这样的查询，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？ 谢谢！ 克里斯

Answer 1

试试这个：

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：这是没有意义的项目一年顺序您已经在它聚集。

Answer 2

尝试以下

SELECT 
    country as "Recipient", 
    SUM(case WHEN project_year = 1991 then usd_amount else 0 end) AS "1991" , 
    SUM(case WHEN project_year = 1992 then usd_amount else 0 end) AS "1992" , 
    SUM(case WHEN project_year = 1993 then usd_amount else 0 end) AS "1993" 

FROM tb1 

GROUP BY country, project_year 
order by country, project_year