问题描述
如果已知irt_tlevel列中不同值的数量是固定的，则可以使用条件聚合。
select
extract(year from a.created) as Year,
a.testscoreid,
sum(case when b.irt_tlevel = 'Low' then 1 else 0 end) as Low,
sum(case when b.irt_tlevel = 'Medium' then 1 else 0 end) as Medium,
sum(case when b.irt_tlevel = 'High' then 1 else 0 end) as High,
count(*) as Questions
from asmt.testscores a
join asmt.questions b on a.questionid = b.questionid
where a.answered = True
group by Year, a.testscoreid
order by Year desc, a.testscoreid
解决方法
我有一个Postgres带有通常group by子句的（）查询：
select extract(year from a.created) as Year,a.testscoreid,b.irt_tlevel,count(a.*) as Questions
from asmt.testscores a join asmt.questions b
on a.questionid = b.questionid
where a.answered = True
group by Year,b.irt_tlevel
order by Year desc,a.testscoreid
该列b.irt_tlevel具有low，medium和值，high所有这些结果均为行格式，例如：
Year TestScoreId Irt_tlevel Questions
2015 1 Low 2
2015 1 Medium 3
2015 1 High 5
我希望我的结果采用以下格式：
Year TestScoreId Low Medium High TotalQuestions
2015 1 2 3 5 10
任何帮助，将不胜感激。