sql - 如何将两个 postgres 列合并为单个值(json 对象)

Question

我正尝试在我的 food.list 表上编写查询:

categories    | items
----------------------------
dairy         | ["milk", "cheese"]
fruit         | ["apples", "pears", "grapes"]
vegetables    | ["carrots"]  

并返回一个只有一行的 selected_foods 列。我希望该行的值是一个包含类别(键)列表和项目(值)数组的对象。

selected_foods
------------------------------------
{ 
  dairy: ["milk", "cheese"], 
  fruit: ["apples", "pears", "grapes"], 
  vegetables: ["carrots"] 
}

到目前为止，我已经尝试过:

SELECT json_agg(json_build_object(categories, items::json))::json 
AS selected_foods
FROM food.list

但这会返回一个对象数组，即:

selected_foods
------------------------------------
[ 
  { dairy: ["milk", "cheese"] }, 
  { fruit: ["apples", "pears", "grapes"] }, 
  { vegetables: ["carrots"] }
]

我想我太早应用了 json_build_object 函数......或者我可能需要在之后再次打开它们？

任何帮助都会很棒，谢谢 :)

Answer 1

使用json_object_agg

SELECT json_object_agg( categories, items::json)  as selected_foods
     from list 

DEMO