我有一个名为STUDENTS的APACHE DERBY数据库表,其中包含以下行:
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| NAME |COUNTER| MONTH |
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| bill | 10 | January |
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| bill | 12 | February|
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| bill | 11 | March |
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| sam | 14 | January |
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| sam | 9 | February|
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| sam | 22 | March |
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| hal | 21 | January |
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| hal | 18 | February|
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| hal | 19 | March |
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我正在尝试找到语法以获得以下输出...
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| NAME | JAN | FEB | MAR |
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| bill | 10 | 12 | 11 |
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| sam | 14 | 9 | 22 |
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| hal | 21 | 18 | 19 |
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我尝试了以下方法:
select distinct(name),
(SELECT COUNTER FROM STUDENTS WHERE NAME = 'bill' AND month = 'january') as jan,
(SELECT COUNTER FROM STUDENTS WHERE NAME = 'bill' AND month = 'february') as feb,
(SELECT COUNTER FROM STUDENTS WHERE NAME = 'bill' AND month = 'march') as mar
FROM STUDENT where name = 'bill'
。它在某种程度上可以作为一个学生的概念证明。但是,它很冗长,它仅适用于一个学生,并且它不能针对来自我将添加到数据库的未来月份。这意味着,我希望能够为每个 NAME 获取最后 3 个 COUNTER 值,无论数据库中有多少个月的数据退出。
我已经查看了多个与嵌套查询相关的 s.o. 问题,但没有一个有帮助。
建议?
任何帮助不胜感激!
您可以使用条件聚合
SELECT name,
Max(CASE WHEN month = 'January' THEN counter end) AS jan,
Max(CASE WHEN month = 'February' THEN counter end) AS feb,
Max(CASE WHEN month = 'March' THEN counter end) AS mar
FROM student
GROUP BY name