从PostgreSQL表中选择数组的JSON对象

Question

我准备了一个简单的SQL Fiddle来证明我的问题 -

在双人游戏中，我将用户聊天存储在表格中：

CREATE TABLE chat(
    gid integer,            /* game id */
    uid integer,            /* user id */
    created timestamptz,
    msg text
);

在这里，我用一个简单的测试数据填充表格：

INSERT INTO chat(gid, uid, created, msg) VALUES
    (10, 1, NOW() + interval '1 min', 'msg 1'),
    (10, 2, NOW() + interval '2 min', 'msg 2'),
    (10, 1, NOW() + interval '3 min', 'msg 3'),
    (10, 2, NOW() + interval '4 min', 'msg 4'),
    (10, 1, NOW() + interval '5 min', 'msg 5'),
    (10, 2, NOW() + interval '6 min', 'msg 6'),
    (20, 3, NOW() + interval '7 min', 'msg 7'),
    (20, 4, NOW() + interval '8 min', 'msg 8'),
    (20, 4, NOW() + interval '9 min', 'msg 9');

我可以通过运行SELECT查询来获取数据：

SELECT ARRAY_TO_JSON(
  COALESCE(ARRAY_AGG(ROW_TO_JSON(x)), 
           array[]::json[])) FROM (
SELECT
    gid,
    uid,
    EXTRACT(EPOCH FROM created)::int AS created,
    msg
FROM chat) x;

它返回一个JSON数组：

[{"gid":10,"uid":1,"created":1514813043,"msg":"msg 1"},
 {"gid":10,"uid":2,"created":1514813103,"msg":"msg 2"},
 {"gid":10,"uid":1,"created":1514813163,"msg":"msg 3"},
 {"gid":10,"uid":2,"created":1514813223,"msg":"msg 4"},
 {"gid":10,"uid":1,"created":1514813283,"msg":"msg 5"},
 {"gid":10,"uid":2,"created":1514813343,"msg":"msg 6"},
 {"gid":20,"uid":3,"created":1514813403,"msg":"msg 7"},
 {"gid":20,"uid":4,"created":1514813463,"msg":"msg 8"},
 {"gid":20,"uid":4,"created":1514813523,"msg":"msg 9"}]

这接近我的需要，但我想使用“gid”作为JSON对象属性，其余数据作为该对象中的值：

{"10": [{"uid":1,"created":1514813043,"msg":"msg 1"},
        {"uid":2,"created":1514813103,"msg":"msg 2"},
        {"uid":1,"created":1514813163,"msg":"msg 3"},
        {"uid":2,"created":1514813223,"msg":"msg 4"},
        {"uid":1,"created":1514813283,"msg":"msg 5"},
        {"uid":2,"created":1514813343,"msg":"msg 6"}],

 "20": [{"uid":3,"created":1514813403,"msg":"msg 7"},
        {"uid":4,"created":1514813463,"msg":"msg 8"},
        {"uid":4,"created":1514813523,"msg":"msg 9"}]}

请问使用PostgreSQL JSON functions可以吗？

Answer 1

我认为你正在为最后一步寻找json_object_agg。我是这样做的：

SELECT  json_object_agg(
          gid::text, array_to_json(ar)
        )
FROM    (
  SELECT  gid,
          array_agg(
            json_build_object(
              'uid', uid,
              'created', EXTRACT(EPOCH FROM created)::int,
              'msg', msg)
          ) AS ar
  FROM    chat
  GROUP BY gid
) x
;

我离开了coalesce因为我不认为空阵列是可能的。但是，如果您的真实查询更复杂，可能需要它，那么应该很容易。