WINDOW FUNCTION FIRST_VALUE

description

FIRST_VALUE() 返回窗口范围内的第一个值。

FIRST_VALUE(expr) OVER(partition_by_clause order_by_clause [window_clause])

example

我们有如下数据

 select name, country, greeting from mail_merge;
 | name    | country | greeting     |
 |---------|---------|--------------|
 | Pete    | USA     | Hello        |
 | John    | USA     | Hi           |
 | Boris   | Germany | Guten tag    |
 | Michael | Germany | Guten morgen |
 | Bjorn   | Sweden  | Hej          |
 | Mats    | Sweden  | Tja          |

使用 FIRST_VALUE()，根据 country 分组，返回每个分组中第一个 greeting 的值：

select country, name,    
first_value(greeting)    
over (partition by country order by name, greeting) as greeting from mail_merge;
| country | name    | greeting  |
|---------|---------|-----------|
| Germany | Boris   | Guten tag |
| Germany | Michael | Guten tag |
| Sweden  | Bjorn   | Hej       |
| Sweden  | Mats    | Hej       |
| USA     | John    | Hi        |
| USA     | Pete    | Hi        |

keywords

WINDOW,FUNCTION,FIRST_VALUE