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