postgresql获取每组前几条记录

postgresql获取每组前几条记录：

示例

表结构如下：

               Table "ytt.t1"  
 Column |         Type          | Modifiers   
--------+-----------------------+-----------  
 i_name | character varying(10) | not null  
 rank   | integer               | not null

模拟了20条数据来做演示：

t_girl=# select * from t1 order by i_name; 
 i_name  | rank   
---------+------  
 Charlie |   12  
 Charlie |   12  
 Charlie |   13  
 Charlie |   10  
 Charlie |   11  
 Lily       |    6  
 Lily       |    7  
 Lily        |    7  
 Lily       |    6  
 Lily       |    5  
 Lily    |    7  
 Lily    |    4  
 Lucy    |    1  
 Lucy    |    2  
 Lucy    |    2  
 Ytt     |   14  
 Ytt     |   15  
 Ytt     |   14  
 Ytt     |   14  
 Ytt     |   15  
(20 rows)

按照人名分组，每组取3条记录：

select * 
from (select i_name, rank, row_number() over(partition by i_name) as row from t1) t
where row < =3

SELECT 语句用于从数据库中选取数据。

结果被存储在一个结果表中，称为结果集。

SQL SELECT 语法

SELECT column_name,column_name
FROM table_name;

与

SELECT * FROM table_name;

SQL WHERE 子句

WHERE 子句用于提取那些满足指定条件的记录。

SQL WHERE 语法

SELECT column_name,column_name
FROM table_name
WHERE column_name operator value;

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