Query table with array_agg of ALL previous positio

问题:

I have a database table with:

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

How can I query the table efficiently so that I can get a new column using array_agg().

I have already tried the following query however its incredibly slow and also wrong as it doesn't group the previous_positions by the name column:

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

I expect the table output to look like this

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}

回答1:

You may use the WINDOW clause for 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