PostgreSQL 根据其他 2 列填充一列

Question

我在 Postgres 10.4 中有下表。

Name   Email          EmailType 
--------------------------------------      
John   [email protected]   Primary Email   
John   [email protected]   Secondary Email
John   [email protected]  Work Email
Jack   [email protected]   Primary Email   
Jack   [email protected]   Secondary Email
Jim    [email protected]    Primary Email   

如何根据名称（假设该名称在此表中是唯一的）和电子邮件类型列中的值在 col4 中分配值。对于每个人（

Name

列），我想检查他们有多少电子邮件类型（

EmailType

列），然后将人名和电子邮件类型连接到一个新列中。 像下面这样。

Name   Email          EmailType         Col4
-----------------------------------------------------------------------------------------
John   [email protected]   Primary Email     John: Primary Email, Secondary Email, Work Email
John   [email protected]   Secondary Email
John   [email protected]  Work Email
Jack   [email protected]   Primary Email     Jack: Primary Email, Secondary Email
Jack   [email protected]   Secondary Email
Jim    [email protected]    Primary Email     Jim: Primary Email

我想过使用

CASE

语句，但无法让它发挥作用。对此的任何帮助将不胜感激。

Answer 1

您可以使用窗口函数和字符串聚合来做到这一点。

select name, email, emailtype, 
 case when rn = 1 then string_agg(emailtype, ', ') over (partition by name) end col4
from
(
 select *, row_number() over (partition by name order by emailtype) rn from the_table
) t;

数据库小提琴

正如@jarlh 评论的那样，使用视图。