Question

我想在分组时将两列聚合成一个“数组”。

假设一个像这样的表：

friends_map:
=================================
user_id    friend_id    confirmed
=================================
1          2            true
1          3            false
2          1            true
2          3            true
1          4            false

我想从user_id中选择此表和group并获取friend_id并确认为以逗号分隔的连接值。

目前我有这个：

SELECT user_id, array_agg(friend_id) as friends, array_agg(confirmed) as confirmed
FROM friend_map
WHERE user_id = 1
GROUP BY user_id

让我：

=================================
user_id    friends      confirmed
=================================
1         [2,3,4]       [t, f, f]

我怎样才能得到：

=================================
user_id    friends     
=================================
1         [ [2,t], [3,f], [4,f] ]

Answer 1

SELECT user_id, array_agg((friend_id, confirmed)) as friends
FROM friend_map
WHERE user_id = 1
GROUP BY user_id

user_id |           array_agg            
--------+--------------------------------
      1 | {"(2,true)","(3,false)","(4,false)"}

Answer 2

你可以避免多维数组的丑陋并使用一些支持混合数据类型的json：

SELECT user_id, json_agg(json_build_array(friend_id, confirmed)) AS friends 
    FROM friends_map 
    WHERE user_id = 1
    GROUP BY user_id

或者使用一些key : value对，因为json允许，所以如果你愿意，你的输出将更多 semantic ：

SELECT user_id, json_agg(json_build_object(
        'friend_id', friend_id, 
        'confirmed', confirmed
    )) AS friends 
    FROM friends_map 
    WHERE user_id = 1
    GROUP BY user_id;

Answer 3

您可以在将这些值合并到array_agg()函数之前将它们连接在一起：

SELECT user_id, array_agg('[' || friend_id || ',' || confirmed || ']') as friends
FROM friends_map
WHERE user_id = 1
GROUP BY user_id

演示：SQL Fiddle

Answer 4

在 Postgres 9.5 中，您可以获取文本数组：

SELECT user_id, array_agg(array[friend_id::text, confirmed::text])
FROM friend_map
WHERE user_id = 1
GROUP BY user_id;

 user_id |           array_agg            
---------+--------------------------------
       1 | {{2,true},{3,false},{4,false}}
(1 row)

或int数组数组：

SELECT user_id, array_agg(array[friend_id, confirmed::int])
FROM friend_map
WHERE user_id = 1
GROUP BY user_id;

 user_id |      array_agg      
---------+---------------------
       1 | {{2,1},{3,0},{4,0}}
(1 row)

Answer 5

您可以使用：array[]

只需这样做：

SELECT user_id, array[friend_id, confirmed]
FROM friend_map
WHERE user_id = 1
GROUP BY 1;

Postgres - 将两列聚合成一个项目

5 个答案: