PostgreSQL，聚合和组合

Question

我在 PostgreSQL 中有一个 table：

name TEXT,
country_code TEXT
visited TIMESTAMP

我知道country_code只能是US、UK或CH。

我想要类似于以下的输出：

name,  US-last-visited, UK-last-visited, CH-last-visited
Gregg  null             2022-01-02       2001-01-02
Paul   1999-01-10       null             2021-01-03

可以用例如GROUP BY 和 ARRAY_AGG 或类似的？

Answer 1

您可以使用条件聚合：

select name
     , max(case when country_code = 'US' then visited end) as US_last_visited
     , max(case when country_code = 'UK' then visited end) as UK_last_visited
     , max(case when country_code = 'CH' then visited end) as CH_last_visited
from t
group by name

Answer 2

您可以使用过滤聚合：

select name, 
       max(visited) filter (where country_code = 'UK') as uk_last_visited,
       max(visited) filter (where country_code = 'US') as us_last_visited,
       max(visited) filter (where country_code = 'CH') as ch_last_visited
from the_table
group by name

PostgreSQL，聚合和组合

PostgreSQL, aggregate and combine

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postgresql

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