postgreSQL分组查询中位数，偶数行输出中间两条记录

需求：

多条记录中按姓名分组，分组后的结果取中位数，若同一组记录行数为基数，打印正中间记录；若同一组记录行数为偶数，打印中间两条记录

结果

查询sql：

with Graduates as   --创建虚表并添加记录，表名为：Graduates
(
select '2022-01' as period,'迈克' as name ,40 as income
union select '2022-02' as period,'迈克' as name ,30 as income
union select '2022-01' as period,'阿诺德' as name ,20 as income
union select '2022-02' as period,'阿诺德' as name ,25 as income
union select '2022-02' as period,'阿诺德' as name ,35 as income
union select '2022-01' as period,'劳伦斯' as name ,10 as income
union select '2022-02' as period,'劳伦斯' as name ,18 as income
union select '2022-03' as period,'劳伦斯' as name ,5 as income
union select '2022-04' as period,'劳伦斯' as name ,3 as income
)

select t.name,percentile_disc(0.5) within group (order by income)  as rn from Graduates t 
group by t.name
union
select t.name,percentile_disc(0.51) within group (order by income)  as rn from Graduates t
group by t.name
;

补充：

1.percentile_disc(0.5) within group (order by income) 表示取中位数
2.percentile_disc函数，表示最接近请求百分位的离散值，传参0.5即50%，如果有偶数行，0.5默认把小的中位数取出来，传参0.51把偶数行较大的中位数取出来，并集结果输出。