我已经为我的问题准备了一个SQL Fiddle -
给定以下表格:
CREATE TABLE chat(
gid integer, /* game id */
uid integer, /* user id */
created timestamptz,
msg text
);
填充以下测试数据:
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');
我可以使用以下查询:
SELECT json_object_agg(
gid, array_to_json(y)
) FROM (
SELECT gid,
array_agg(
json_build_object(
'uid', uid,
'created', EXTRACT(EPOCH FROM created)::int,
'msg', msg)
) y
FROM chat
GROUP BY gid /*, created
ORDER BY created ASC */
) x;
用 "gid" 作为键和数组值,获取表记录的 JSON 对象:
{ "20" : [
{"uid" : 3, "created" : 1514889490, "msg" : "msg 7"},
{"uid" : 4, "created" : 1514889550, "msg" : "msg 8"},
{"uid" : 4, "created" : 1514889610, "msg" : "msg 9"}
],
"10" : [
{"uid" : 1, "created" : 1514889130, "msg" : "msg 1"},
{"uid" : 2, "created" : 1514889190, "msg" : "msg 2"},
{"uid" : 1, "created" : 1514889250, "msg" : "msg 3"},
{"uid" : 2, "created" : 1514889310, "msg" : "msg 4"},
{"uid" : 1, "created" : 1514889370, "msg" : "msg 5"},
{"uid" : 2, "created" : 1514889430, "msg" : "msg 6"}
] }
然而我还缺少一个小东西,就是无法弄清楚:需要按“created”对数组进行排序。因此,我在上面的查询中添加了
ORDER BY created ASC
,同时还必须添加 GROUP BY gid, created
(您可以在上面的查询中看到有问题的代码作为注释)。这会导致 array_agg
出现问题,并导致结果为 1 元素数组(并覆盖重复的“gid”键,当从我的自定义存储函数返回为 jsonb
时)。{ "10": [{ "uid":2, "created":1514889800, "msg":"msg 6" }],
"20": [{ "uid":4, "created":1514889980, "msg":"msg 9" }] }
这里是否可以进行订购,或者我应该在我的JAVA应用程序中处理?