[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
我試圖為我的問題准備一個SQL Fiddle-
在多人文字游戲中,活動游戲存儲在表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
);
選擇所有ID為1
的玩家參與的游戲很容易:
SELECT * FROM words_games WHERE player1 = 1 OR player2 = 1;
但是現在我還添加了一個表words_moves
,它充當玩家動作的日志日志 :
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 */
);
現在,當用戶連接到我的游戲服務器時,我不僅希望向她發送所有活動的游戲,而且還希望向她發送每個游戲的最新動作( mid
最高)。
請問如何在一個查詢中運行這樣的聯接(或CTE)?
我嘗試了以下INNER JOIN,但它返回了所有動作,而我只需要每局中的最新動作:
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:
實際上,我需要左加入,因為有些游戲可能還沒有任何玩家移動。
好的,讓我們構建sql。 首先,我們需要找出所有游戲的最新動作。 有很多方法可以做到這一點,但讓我們嘗試一下:
SELECT *
FROM words_moves wm1
WHERE
played = (SELECT max(played)
FROM words_moves wm2
WHERE wm1.gid = wm2.gid);
這不是最快的方法,但是它是更容易理解的方法之一-從時間戳最近的words_moves
中獲取所有動作。
現在我們有了它,我們可以使用它來構建查詢以獲取游戲和動作:
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,則WITH
表示公共表表達式 ,這是一種非常方便的子查詢。 除其他外,這意味着如果您最終使用不同的方法來獲取每場比賽的最新舉動( 此問題有很多可供選擇的替代方法可供嘗試),那么很容易進行調入而不會帶來太多麻煩。
希望有幫助!
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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