内部結合テーブルで行を数える
3つのテーブルがあります。
プレイヤー：
mysql> SELECT * FROM players;
+-----------+---------+----------------------+----------------------+-----------------+------------------------------+-----------------------+---------------------+
| player_id | team_id | player_name | player_jersey_number | player_position | player_email | player_contact_number | player_timestamp |
+-----------+---------+----------------------+----------------------+-----------------+------------------------------+-----------------------+---------------------+
| 1 | 4 | Popoy Alfonso | 2 | | [email protected] | 09263453234 | 2015-08-05 00:48:10 |
| 2 | 4 | Karlo Ripas | 10 | | [email protected] | 09212354324 | 2015-08-05 00:50:03 |
| 3 | 4 | VHaughn Von | 32 | | [email protected] | 09361234565 | 2015-08-05 00:51:00 |
| 4 | 4 | Lordie Zalbahe | 23 | | [email protected] | 09391222334 | 2015-08-05 00:52:42 |
| 5 | 4 | Jigs Selda | 8 | | [email protected] | 09325566323 | 2015-08-05 00:53:36 |
| 6 | 4 | Rhan Garniel | 3 | | [email protected] | 09129503400 | 2015-08-05 00:54:20 |
| 7 | 5 | Johnritz Rodriguez | 11 | | [email protected] | 09231112346 | 2015-08-05 00:56:02 |
| 8 | 5 | Garret Van Sarmiento | 7 | | [email protected] | 09264565600 | 2015-08-05 00:56:53 |
| 9 | 5 | Lester Selda Lineses | 12 | | [email protected] | 09068746354 | 2015-08-05 00:57:47 |
| 10 | 5 | Laurence Lineses | 44 | | [email protected] | 09847354672 | 2015-08-05 00:59:33 |
| 11 | 5 | Xandrix Buendia | 1 | | [email protected] | 09234665590 | 2015-08-05 01:00:12 |
| 12 | 5 | Betoyskie Limpiada | 45 | | [email protected] | 09213456667 | 2015-08-05 01:01:15 |
+-----------+---------+----------------------+----------------------+-----------------+------------------------------+-----------------------+---------------------+
チーム：
mysql> SELECT * FROM teams;
+---------+-----------+----------------------+---------------------+
| team_id | season_id | team_name | team_timestamp |
+---------+-----------+----------------------+---------------------+
| 4 | 1 | Quiapo A | 2015-08-05 00:30:13 |
| 5 | 1 | Quiapo B | 2015-08-05 00:30:25 |
| 6 | 1 | Balik-Balik Warriors | 2015-08-05 00:31:13 |
| 7 | 1 | Adamson Falcons | 2015-08-05 00:31:42 |
| 8 | 1 | Pasay Flooders | 2015-08-05 00:32:04 |
| 9 | 1 | Marina Dragons | 2015-08-05 00:32:22 |
| 10 | 1 | MDC Archers | 2015-08-05 00:33:12 |
| 11 | 2 | Quiapo A | 2015-08-05 00:34:25 |
| 12 | 2 | Quiapo B | 2015-08-05 00:34:38 |
| 13 | 2 | Marikina Eagels | 2015-08-05 00:35:11 |
| 14 | 2 | TIP Steallers | 2015-08-05 00:35:32 |
| 15 | 2 | Gasan Blue Eagles | 2015-08-05 00:36:12 |
+---------+-----------+----------------------+---------------------+
季節：
mysql> SELECT * FROM seasons;
+-----------+-------------+----------------------+---------------------+
| season_id | season_name | season_event_name | season_timestamp |
+-----------+-------------+----------------------+---------------------+
| 1 | Season 1 | Summer Games | 2015-08-05 00:23:15 |
| 2 | Season 2 | Aniversary Sportfest | 2015-08-05 00:25:10 |
+-----------+-------------+----------------------+---------------------+
私は現在このクエリに取り組んでいますが、結果は正しくありません。
SELECT
teams.team_name,
(
SELECT COUNT(*)
FROM teams
INNER JOIN players
ON teams.team_id = players.team_id
) as num_of_players,
teams.team_timestamp
FROM teams
INNER JOIN seasons
ON seasons.season_id = teams.season_id
GROUP BY teams.team_name;
出力：
+----------------------+----------------+---------------------+
| team_name | num_of_players | team_timestamp |
+----------------------+----------------+---------------------+
| Adamson Falcons | 12 | 2015-08-05 00:31:42 |
| Balik-Balik Warriors | 12 | 2015-08-05 00:31:13 |
| Gasan Blue Eagles | 12 | 2015-08-05 00:36:12 |
| Marikina Eagels | 12 | 2015-08-05 00:35:11 |
| Marina Dragons | 12 | 2015-08-05 00:32:22 |
| MDC Archers | 12 | 2015-08-05 00:33:12 |
| Pasay Flooders | 12 | 2015-08-05 00:32:04 |
| Quiapo A | 12 | 2015-08-05 00:30:13 |
| Quiapo B | 12 | 2015-08-05 00:30:25 |
| TIP Steallers | 12 | 2015-08-05 00:35:32 |
+----------------------+----------------+---------------------+
私が欲しい結果はこれです：
+----------------------+----------------+---------------------+
| team_name | num_of_players | team_timestamp |
+----------------------+----------------+---------------------+
| Adamson Falcons | 0 | 2015-08-05 00:31:42 |
| Balik-Balik Warriors | 0 | 2015-08-05 00:31:13 |
| Gasan Blue Eagles | 0 | 2015-08-05 00:36:12 |
| Marikina Eagels | 0 | 2015-08-05 00:35:11 |
| Marina Dragons | 0 | 2015-08-05 00:32:22 |
| MDC Archers | 0 | 2015-08-05 00:33:12 |
| Pasay Flooders | 0 | 2015-08-05 00:32:04 |
| Quiapo A | 6 | 2015-08-05 00:30:13 |
| Quiapo B | 6 | 2015-08-05 00:30:25 |
| TIP Steallers | 0 | 2015-08-05 00:35:32 |
+----------------------+----------------+---------------------+
完全に整理された答え。
プレーヤーとチームのテーブルにいくつかのデータを追加して、回答をより一般的なものにしました-この回答で使用されているすべてのDDL（CREATE TABLE tab_name...）とDML（INSERT INTO tab_name VALUES...）については、投稿の下部を参照してください。また、シーズンテーブル（OPから変更されていない、つまりあなたの）の元のデータも作成しました。
ところで、フォーラムへようこそ。しかし、あなたは本当に私たちにDDLとDMLを与えたはずです。ページの左下にあるツアーと「私たちがあなたを助けるためにどのように役立つか」のブログもご覧ください。しかし、私は興味を持って自分でやりましたが、DDLとDMLを提供すれば、もっと多くの人に手伝ってもらえるでしょう。
テーブルを作成してロードした後、次のSQLを実行しました。
SELECT t1.team_name,
IFNULL(t2.num_players, 0) AS strength,
t1.team_timestamp
FROM team t1
LEFT OUTER JOIN
(SELECT team_id, COUNT(team_id) AS num_players
FROM player
GROUP BY team_id
) t2
ON t1.team_id = t2.team_id
-- GROUP BY t1.team_id, t1.team_name, t1.season_id -- **NOTE** - see discussion below
ORDER BY strength DESC, team_name ASC;
そして、結果はあなたが望むものではありませんが、近いです。
+----------------------+----------+---------------------+
| team_name | strength | team_timestamp |
+----------------------+----------+---------------------+
| Quiapo B | 7 | 2015-08-05 00:30:25 |
| Quiapo B | 7 | 2015-08-05 00:30:25 |
| Quiapo A | 6 | 2015-08-05 00:30:13 |
| Quiapo A | 6 | 2015-08-05 00:30:13 |
| Adamson Falcons | 0 | 2015-08-05 00:31:42 |
| Balik-Balik Warriors | 0 | 2015-08-05 00:31:13 |
| Gasan Blue Eagles | 0 | 2015-08-05 00:36:12 |
| Marikina Eagels | 0 | 2015-08-05 00:35:11 |
| Marina Dragons | 0 | 2015-08-05 00:32:22 |
| MDC Archers | 0 | 2015-08-05 00:33:12 |
| Pasay Flooders | 0 | 2015-08-05 00:32:04 |
| TIP Steallers | 0 | 2015-08-05 00:35:32 |
+----------------------+----------+---------------------+
ONareのクエリを実行すると、（！）
+-----------+----------------+---------------------+
| team_name | num_of_players | team_timestamp |
+-----------+----------------+---------------------+
| Quiapo A | 26 | 2015-08-05 00:30:13 |
+-----------+----------------+---------------------+
26 = 2 *（6 + 7）であることに注意してください。ただし、sql_modeがSTRICT_TRANS_TABLES,NO_ENGINE_SUBSTITUTION,ONLY_FULL_GROUP_BYに設定されている場合、このクエリは失敗し、次のメッセージが表示されます
ERROR 1140 (42000): Mixing of GROUP columns (MIN(),MAX(),COUNT(),...) with no GROUP columns is illegal if there is no GROUP BY clause
ただし、oNareのクエリを少し変更すると、最初のクエリで取得したのと同じ結果が得られます（sql_modeがONLY_FULL_GROUP_BYに設定されていない場合）。
SELECT
team.team_name,
COUNT(player.player_id) as num_of_players,
team.team_timestamp
FROM team
LEFT JOIN player ON (player.team_id = team.team_id)
LEFT JOIN seasons ON (seasons.season_id = team.season_id)
GROUP BY team.team_name, team.season_id, team.team_timestamp -- **ADDED**
ORDER BY num_of_players DESC, team.team_name ASC;
GROUP BYを追加すると、正しい答えが得られます。興味深いことに、GROUP BY行がコメント化されている場合、PostgreSQLはエラーをスローします。 GROUP BY行の直前にORDER BY行を追加しないと、PostgreSQLでもクエリが機能しません。
一般的な回答として、どちらの回答もあなたの質問に対して正しいものとして受け入れることができます（GROUP BYを使用）。表の詳細情報がないと、希望する結果を得ることができませんが、以下を参照してください。
余談ですが、ONLY_FULL_GROUP_BYは 5.7のデフォルトモード になるので、今すぐ取得することもできます。
私はあなたのテーブル構造にいくらかの修正が必要だと思います。季節ごとにプレーヤーを配置する必要があります（理にかなっています、移籍）。異なるシーズンの同じチームで同じidsを使用する必要があります-そうでない場合、どのようにして多くのシーズンの統計（ゴール/ポイント/マッチウォン/ロスト）を集計しますか？
表DDLおよびDML-構造および内容
CREATE TABLE player (player_id INT, team_id INT, player_name VARCHAR(25));
CREATE TABLE team( team_id INT, season_id INT, team_name VARCHAR(25), team_timestamp TIMESTAMP);
CREATE TABLE season (season_id INT, season_name VARCHAR(25));
INSERT INTO player VALUES (1, 4, 'Popoy Alfonso');
INSERT INTO player VALUES (2, 4, 'Karlo Ripas');
INSERT INTO player VALUES (3, 4, 'VHaughn Von');
INSERT INTO player VALUES (4, 4, 'Lordie Zalbahe');
INSERT INTO player VALUES (5, 4, 'Jigs Selda' );
INSERT INTO player VALUES (6, 4, 'Rhan Garniel' );
INSERT INTO player VALUES (7, 5, 'Johnritz Rodriguez' );
INSERT INTO player VALUES (8, 5, 'Garret Van Sarmiento');
INSERT INTO player VALUES (9, 5, 'Lester Selda Lineses');
INSERT INTO player VALUES (10, 5, 'Laurence Lineses' );
INSERT INTO player VALUES (11, 5, 'Xandrix Buendia' );
INSERT INTO player VALUES (12, 5, 'Betoyskie Limpiada' );
INSERT INTO player VALUES (12, 5, 'Donald Duck' ); -- Added Donald Duck!
-- I inserted extra records into the player table as below.
INSERT INTO player VALUES (1, 11, 'Popoy Alfonso');
INSERT INTO player VALUES (2, 11, 'Karlo Ripas');
INSERT INTO player VALUES (3, 11, 'VHaughn Von');
INSERT INTO player VALUES (11, 11, 'Lordie Zalbahe');
INSERT INTO player VALUES (5, 11, 'Jigs Selda' );
INSERT INTO player VALUES (6, 11, 'Rhan Garniel' );
INSERT INTO player VALUES (7, 12, 'Johnritz Rodriguez' );
INSERT INTO player VALUES (8, 12, 'Garret Van Sarmiento');
INSERT INTO player VALUES (9, 12, 'Lester Selda Lineses');
INSERT INTO player VALUES (10, 12, 'Laurence Lineses' );
INSERT INTO player VALUES (11, 12, 'Xandrix Buendia' );
INSERT INTO player VALUES (12, 12, 'Betoyskie Limpiada' );
チームテーブルの場合、シーズン1とシーズン2でQuiradoAとQuiradoBに同じidを指定しました-シーズンが変わるという理由だけで同じチームに異なるidsを指定しても意味がありません。また、QuiradoAとBでも同じTIMESTAMPを保持しました。
INSERT INTO team VALUES ( 4 , 1 , 'Quiapo A' , '2015-08-05 00:30:13');
INSERT INTO team VALUES ( 5 , 1 , 'Quiapo B' , '2015-08-05 00:30:25');
INSERT INTO team VALUES ( 6 , 1 , 'Balik-Balik Warriors' , '2015-08-05 00:31:13');
INSERT INTO team VALUES ( 7 , 1 , 'Adamson Falcons' , '2015-08-05 00:31:42');
INSERT INTO team VALUES ( 8 , 1 , 'Pasay Flooders' , '2015-08-05 00:32:04');
INSERT INTO team VALUES ( 9 , 1 , 'Marina Dragons' , '2015-08-05 00:32:22');
INSERT INTO team VALUES ( 10 , 1 , 'MDC Archers' , '2015-08-05 00:33:12');
INSERT INTO team VALUES ( 4 , 2 , 'Quiapo A' , '2015-08-05 00:30:13'); -- **NOTE** `id` and `TIMESTAMP` for both A & B.
INSERT INTO team VALUES ( 5 , 2 , 'Quiapo B' , '2015-08-05 00:30:25');
INSERT INTO team VALUES ( 13 , 2 , 'Marikina Eagels' , '2015-08-05 00:35:11');
INSERT INTO team VALUES ( 14 , 2 , 'TIP Steallers' , '2015-08-05 00:35:32');
INSERT INTO team VALUES ( 15 , 2 , 'Gasan Blue Eagles' , '2015-08-05 00:36:12');
INSERT INTO season VALUES(1, 'Season 1');
INSERT INTO season VALUES(2, 'Season 2');
クエリで12 _num_of_players_が返されます。サブクエリだけが行を返したため、SELECT COUNT(*) FROM teams INNER JOIN players ON teams.team_id = players.team_id;を実行すると、実際に何が行われているのかがわかります。
構文を修正するには、もう1つ_LEFT JOIN_を使用します。
_SELECT
teams.team_name,
COUNT(players.player_id) as num_of_players,
teams.team_timestamp
FROM test.teams
LEFT JOIN test.players ON (players.team_id=teams.team_id)
LEFT JOIN test.seasons ON (seasons.season_id = teams.season_id)
GROUP BY teams.team_name;
_テスト情報：
_mysql> SELECT * FROM test.players;
+-----------+---------+--------------------+----------------------+-----------------+--------------+-----------------------+------------------+
| player_id | team_id | player_name | player_jersey_number | player_position | player_email | player_contact_number | player_timestamp |
+-----------+---------+--------------------+----------------------+-----------------+--------------+-----------------------+------------------+
| 1 | 4 | Popoy Alfonso | 2 | NULL | NULL | NULL | NULL |
| 2 | 4 | NULL | 10 | NULL | NULL | NULL | NULL |
| 3 | 4 | NULL | NULL | NULL | NULL | NULL | NULL |
| 4 | 4 | NULL | NULL | NULL | NULL | NULL | NULL |
| 5 | 4 | NULL | NULL | NULL | NULL | NULL | NULL |
| 6 | 4 | NULL | NULL | NULL | NULL | NULL | NULL |
| 7 | 5 | Johnritz Rodriguez | 11 | NULL | NULL | NULL | NULL |
| 8 | 5 | NULL | NULL | NULL | NULL | NULL | NULL |
| 9 | 5 | NULL | NULL | NULL | NULL | NULL | NULL |
| 10 | 5 | NULL | NULL | NULL | NULL | NULL | NULL |
| 11 | 5 | NULL | NULL | NULL | NULL | NULL | NULL |
| 12 | 5 | NULL | NULL | NULL | NULL | NULL | NULL |
+-----------+---------+--------------------+----------------------+-----------------+--------------+-----------------------+------------------+
12 rows in set (0.00 sec)
mysql> SELECT * FROM test.teams;
+---------+-----------+----------------------+----------------+
| team_id | season_id | team_name | team_timestamp |
+---------+-----------+----------------------+----------------+
| 4 | 1 | Quiapo A | NULL |
| 5 | 1 | Quiapo B | NULL |
| 6 | 1 | Balik-Balik Warriors | NULL |
| 7 | 1 | Adamson Falcons | NULL |
| 8 | 1 | Pasay Flooders | NULL |
| 9 | 1 | Marina Dragons | NULL |
| 10 | 1 | MDC Archers | NULL |
| 11 | 2 | Quiapo A | NULL |
| 12 | 2 | Quiapo B | NULL |
| 13 | 2 | Marikina Eagels | NULL |
| 14 | 2 | TIP Steallers | NULL |
| 15 | 2 | Gasan Blue Eagles | NULL |
+---------+-----------+----------------------+----------------+
12 rows in set (0.00 sec)
mysql> SELECT * FROM test.seasons;
+-----------+-------------+----------------------+------------------+
| season_id | season_name | season_event_name | season_timestamp |
+-----------+-------------+----------------------+------------------+
| 1 | Season 1 | Summer Games | NULL |
| 2 | Season 2 | Aniversary Sportfest | NULL |
+-----------+-------------+----------------------+------------------+
2 rows in set (0.00 sec)
mysql>
_あなたのクエリ：
_mysql> SELECT teams.team_name, (SELECT COUNT(*) FROM teams INNER JOIN players ON teams.team_id = players.team_id) as num_of_players, teams.team_timestamp
-> FROM teams
-> INNER JOIN seasons
-> ON seasons.season_id = teams.season_id
-> GROUP BY teams.team_name;
+----------------------+----------------+----------------+
| team_name | num_of_players | team_timestamp |
+----------------------+----------------+----------------+
| Adamson Falcons | 12 | NULL |
| Balik-Balik Warriors | 12 | NULL |
| Gasan Blue Eagles | 12 | NULL |
| Marikina Eagels | 12 | NULL |
| Marina Dragons | 12 | NULL |
| MDC Archers | 12 | NULL |
| Pasay Flooders | 12 | NULL |
| Quiapo A | 12 | NULL |
| Quiapo B | 12 | NULL |
| TIP Steallers | 12 | NULL |
+----------------------+----------------+----------------+
10 rows in set (0.00 sec)
mysql>
_固定クエリ：
_mysql> SELECT
-> teams.team_name,
-> COUNT(players.player_id) as num_of_players,
-> teams.team_timestamp
-> FROM test.teams
-> LEFT JOIN test.players ON (players.team_id=teams.team_id)
-> LEFT JOIN test.seasons ON (seasons.season_id = teams.season_id)
-> GROUP BY teams.team_name;
+----------------------+----------------+----------------+
| team_name | num_of_players | team_timestamp |
+----------------------+----------------+----------------+
| Adamson Falcons | 0 | NULL |
| Balik-Balik Warriors | 0 | NULL |
| Gasan Blue Eagles | 0 | NULL |
| Marikina Eagels | 0 | NULL |
| Marina Dragons | 0 | NULL |
| MDC Archers | 0 | NULL |
| Pasay Flooders | 0 | NULL |
| Quiapo A | 6 | NULL |
| Quiapo B | 6 | NULL |
| TIP Steallers | 0 | NULL |
+----------------------+----------------+----------------+
10 rows in set (0.00 sec)
mysql>
_ここの出力を参照してください： SQLFiddle