[英]How to select all entries in a table with a subquery counting entries in another table by id from the first query
[英]Select all entries from a table and the LATEST entries from another “logging” table
我试图为我的问题准备一个SQL Fiddle-
在多人文字游戏中,活动游戏存储在表words_games
:
CREATE TABLE words_games (
gid SERIAL PRIMARY KEY, /* game id */
created timestamptz NOT NULL,
player1 integer REFERENCES words_users(uid) ON DELETE CASCADE NOT NULL,
player2 integer REFERENCES words_users(uid) ON DELETE CASCADE,
played1 timestamptz,
played2 timestamptz,
score1 integer NOT NULL CHECK(score1 >= 0),
score2 integer NOT NULL CHECK(score2 >= 0),
hand1 varchar[7] NOT NULL,
hand2 varchar[7] NOT NULL,
pile varchar[116] NOT NULL,
letters varchar[15][15] NOT NULL,
values integer[15][15] NOT NULL,
bid integer NOT NULL REFERENCES words_boards ON DELETE CASCADE
);
选择所有ID为1
的玩家参与的游戏很容易:
SELECT * FROM words_games WHERE player1 = 1 OR player2 = 1;
但是现在我还添加了一个表words_moves
,它充当玩家动作的日志日志 :
CREATE TYPE words_action AS ENUM ('play', 'skip', 'swap', 'resign');
CREATE TABLE words_moves (
mid SERIAL PRIMARY KEY, /* move id */
action words_action NOT NULL,
gid integer NOT NULL REFERENCES words_games ON DELETE CASCADE,
uid integer NOT NULL REFERENCES words_users ON DELETE CASCADE,
played timestamptz NOT NULL,
tiles jsonb NULL,
score integer NULL CHECK(score > 0) /* score awarded in that move */
);
现在,当用户连接到我的游戏服务器时,我不仅希望向她发送所有活动的游戏,而且还希望向她发送每个游戏的最新动作( mid
最高)。
请问如何在一个查询中运行这样的联接(或CTE)?
我尝试了以下INNER JOIN,但它返回了所有动作,而我只需要每局中的最新动作:
SELECT
g.gid,
EXTRACT(EPOCH FROM g.created)::int AS created,
g.player1,
COALESCE(g.player2, 0) AS player2,
COALESCE(EXTRACT(EPOCH FROM g.played1)::int, 0) AS played1,
COALESCE(EXTRACT(EPOCH FROM g.played2)::int, 0) AS played2,
ARRAY_TO_STRING(g.hand1, '') AS hand1,
ARRAY_TO_STRING(g.hand2, '') AS hand2,
-- g.letters,
-- g.values,
m.action,
m.tiles
FROM words_games g INNER JOIN words_moves m
ON g.gid = m.gid
AND ( g.player1 = m.uid OR g.player2 = m.uid )
AND ( g.player1 = 1 OR g.player2 = 1 )
ORDER BY g.gid;
gid | created | player1 | player2 | played1 | played2 | hand1 | hand2 | action | tiles
-----+------------+---------+---------+------------+------------+---------+---------+--------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
1 | 1471794994 | 1 | 2 | 1471868012 | 1471810486 | ПЕАЯСАС | ЖИОБАЯС | play | [{"col": 7, "row": 10, "value": 1, "letter": "Н"}, {"col": 7, "row": 8, "value": 2, "letter": "К"}, {"col": 7, "row": 9, "value": 1, "letter": "И"}, {"col": 7, "row": 7, "value": 2, "letter": "С"}]
1 | 1471794994 | 1 | 2 | 1471868012 | 1471810486 | ПЕАЯСАС | ЖИОБАЯС | play | [{"col": 7, "row": 14, "value": 2, "letter": "К"}, {"col": 7, "row": 13, "value": 1, "letter": "Н"}, {"col": 7, "row": 11, "value": 3, "letter": "У"}, {"col": 7, "row": 12, "value": 2, "letter": "П"}]
1 | 1471794994 | 1 | 2 | 1471868012 | 1471810486 | ПЕАЯСАС | ЖИОБАЯС | play | [{"col": 6, "row": 2, "value": 2, "letter": "П"}, {"col": 6, "row": 3, "value": 1, "letter": "О"}, {"col": 6, "row": 4, "value": 1, "letter": "Е"}, {"col": 6, "row": 5, "value": 5, "letter": "Ж"}, {"col": 6, "row": 6, "value": 5, "letter": "Ы"}, {"col": 6, "row": 7, "value": 2, "letter": "П"}, {"col": 6, "row": 8, "value": 5, "letter": "Ы"}]
2 | 1471795037 | 1 | 2 | 1471806484 | 1471865696 | КЙВГКСМ | ЯРХЖИМН | swap | "А"
2 | 1471795037 | 1 | 2 | 1471806484 | 1471865696 | КЙВГКСМ | ЯРХЖИМН | play | [{"col": 7, "row": 10, "value": 5, "letter": "Ы"}, {"col": 7, "row": 9, "value": 2, "letter": "Д"}, {"col": 7, "row": 8, "value": 1, "letter": "А"}, {"col": 7, "row": 7, "value": 2, "letter": "Л"}]
(5 rows)
更新:
实际上,我需要左加入,因为有些游戏可能还没有任何玩家移动。
好的,让我们构建sql。 首先,我们需要找出所有游戏的最新动作。 有很多方法可以做到这一点,但让我们尝试一下:
SELECT *
FROM words_moves wm1
WHERE
played = (SELECT max(played)
FROM words_moves wm2
WHERE wm1.gid = wm2.gid);
这不是最快的方法,但是它是更容易理解的方法之一-从时间戳最近的words_moves
中获取所有动作。
现在我们有了它,我们可以使用它来构建查询以获取游戏和动作:
WITH last_moves AS (
SELECT *
FROM words_moves wm1
WHERE
played = (SELECT max(played)
FROM words_moves wm2
WHERE wm1.gid = wm2.gid))
SELECT *
FROM words_games wg
LEFT JOIN last_moves lm
ON (wg.gid = lm.gid)
WHERE
player1 = 1 OR
player2 = 1;
如果您不熟悉,则WITH
表示公共表表达式 ,这是一种非常方便的子查询。 除其他外,这意味着如果您最终使用不同的方法来获取每场比赛的最新举动( 此问题有很多可供选择的替代方法可供尝试),那么很容易进行调入而不会带来太多麻烦。
希望有帮助!
SELECT g.gid
, EXTRACT(EPOCH FROM g.created)::int AS created
, g.player1
, COALESCE(g.player2, 0) AS player2
, COALESCE(EXTRACT(EPOCH FROM g.played1)::int, 0) AS played1
, COALESCE(EXTRACT(EPOCH FROM g.played2)::int, 0) AS played2
, ARRAY_TO_STRING(g.hand1, '') AS hand1
, ARRAY_TO_STRING(g.hand2, '') AS hand2
, m.action
, m.tiles
FROM words_games g
LEFT JOIN words_moves m
ON g.gid = m.gid
-- this is redundant: m.gid is a FK
-- AND (g.player1 = m.uid OR g.player2 = m.uid)
AND NOT EXISTS ( -- suppress all-but-the-last
SELECT * FROM words_moves nx
WHERE nx.gid = g.gid -- Same game
-- AND nx.mid > m.mid -- but a higher moveid
-- (assuming ascending move_ids)
-- or: you could use m.played, if that is ascending
AND nx.played > m.played
)
WHERE (g.player1 = 1 OR g.player2 = 1)
ORDER BY g.gid;
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