Question

我有一个数据库表，其中：

id | date       | position | name
--------------------------------------
1  | 2016-06-29 | 9        | Ben Smith
2  | 2016-06-29 | 1        | Ben Smith
3  | 2016-06-29 | 5        | Ben Smith
4  | 2016-06-29 | 6        | Ben Smith
5  | 2016-06-30 | 2        | Ben Smith
6  | 2016-06-30 | 2        | Tom Brown
7  | 2016-06-29 | 4        | Tom Brown
8  | 2016-06-30 | 2        | Tom Brown
9  | 2016-06-30 | 1        | Tom Brown

如何有效查询表，以便可以使用array_agg（）获得新列。

我已经尝试了以下查询，但是它的运行速度非常慢，而且也出错，因为它没有按名称列对previous_positions进行分组：

SELECT 
j.*,
(SELECT array_agg(id) FROM jockeys j2 WHERE j2.id < j.id)
FROM jockeys j

我希望表格输出看起来像这样

id | date       | position | name      | previous_positions
----------------------------------------------------------
1  | 2016-06-29 | 9        | Ben Smith | {}
2  | 2016-06-29 | 1        | Ben Smith | {9}
3  | 2016-06-29 | 5        | Ben Smith | {9,1}
4  | 2016-06-29 | 6        | Ben Smith | {9,1,5}
5  | 2016-06-30 | 2        | Ben Smith | {9,1,5,6}
6  | 2016-06-30 | 2        | Tom Brown | {}
7  | 2016-06-29 | 4        | Tom Brown | {2}
8  | 2016-06-30 | 2        | Tom Brown | {2,4}
9  | 2016-06-30 | 1        | Tom Brown | {2,4,2}

Answer 1

您可以将WINDOW子句用于array_agg

SELECT 
j.* ,  array_agg(position) over w as previous_positions
FROM jockeys j
WINDOW w as
(  partition by name ORDER BY id rows between 
     unbounded preceding and 1 preceding
     )

DEMO

查询表中所有先前位置（不包括当前位置）的array_agg

1 个答案: