Postgres：嵌套聚合JSON

Question

我查询的表格如下：

Spring boot

我想将它从数据库中拉出来：

namespace | key   | value
---------------------------
foo       | bar   | baz
foo       | alpha | beta
gamma     | delta | epsilon

玩{ "foo": { "bar": "baz", "alpha": "beta" }, "gamma": { "delta": "epsilon" } } 并不能让我超越第一级，因为你不允许嵌套聚合函数。但据我所知，我需要在json_object_agg内GROUP BY，但我不确定这是否可行。也许解决方案与GROUP BY s？

有关

Answer 1

with t (namespace, key, value) as (
    values
    ('foo','bar','baz'),('foo','alpha','beta'),('gamma','delta','epsilon')
), s as (
    select namespace, json_object_agg(key, value) as joa
    from t
    group by namespace
)
select json_object_agg(namespace, joa)
from s
;
                                  json_object_agg                                   
------------------------------------------------------------------------------------
 { "foo" : { "bar" : "baz", "alpha" : "beta" }, "gamma" : { "delta" : "epsilon" } }

由于CTE是一个优化障碍，这个版本可能会更快：

with t (namespace, key, value) as (
    values
    ('foo','bar','baz'),('foo','alpha','beta'),('gamma','delta','epsilon')
)
select json_object_agg(namespace, joa)
from (
    select namespace, json_object_agg(key, value) as joa
    from t
    group by namespace
) s