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[https://en.wikipedia.org/wiki/Hierarchical_and_recursive_queries_in_SQL](https://en.wikipedia.org/wiki/Hierarchical_and_recursive_queries_in_SQL)
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> Though MySQL does not support common table expressions there exists a demonstration of WITH RECURSIVE emulation[17] using stored procedures.
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# 以下追記
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> 「obj」カラムと「sort」カラム、この２つを合わせてユニークキーになる
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であれば、そのようにユニークインデックスを作成してやればよいです。
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で、SELECT, UPDATE, INSERT する際にも obj カラムの値を指定してやれば、単一テーブルで実現できます。
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```sql
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mysql> CREATE TABLE test (
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-> id int PRIMARY KEY AUTO_INCREMENT,
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-> text text,
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-> created DATE,
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-> obj int NOT NULL,
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-> sort int NOT NULL,
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-> UNIQUE KEY (obj, sort)
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-> );
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Query OK, 0 rows affected (0.04 sec)
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mysql> INSERT INTO test (text, created, obj, sort) VALUES
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-> ('こんにちは', '2016-12-11', 1, 1),
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-> ('私の名前は太郎です', '2016-12-12', 1, 2),
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-> ('どうぞよろしくお願いします。', '2016-12-13', 1, 3),
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-> ('こんばんは', '2016-12-11', 2, 1),
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-> ('私の名前は花子です', '2016-12-12', 2, 2),
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-> ('どうぞよろしくお願いします。', '2016-12-13', 2, 3);
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Query OK, 6 rows affected (0.01 sec)
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Records: 6 Duplicates: 0 Warnings: 0
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mysql> SELECT * FROM test ORDER BY obj, sort;
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+----+--------------------------------------------+------------+-----+------+
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| id | text | created | obj | sort |
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+----+--------------------------------------------+------------+-----+------+
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| 1 | こんにちは | 2016-12-11 | 1 | 1 |
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| 2 | 私の名前は太郎です | 2016-12-12 | 1 | 2 |
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| 3 | どうぞよろしくお願いします。 | 2016-12-13 | 1 | 3 |
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| 4 | こんばんは | 2016-12-11 | 2 | 1 |
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| 5 | 私の名前は花子です | 2016-12-12 | 2 | 2 |
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| 6 | どうぞよろしくお願いします。 | 2016-12-13 | 2 | 3 |
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+----+--------------------------------------------+------------+-----+------+
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6 rows in set (0.00 sec)
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mysql> BEGIN;
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Query OK, 0 rows affected (0.00 sec)
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mysql> SELECT sort FROM test WHERE obj = 1 AND text = '私の名前は太郎です' FOR UPDATE;
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+------+
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| sort |
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+------+
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| 2 |
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+------+
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1 row in set (0.01 sec)
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mysql> UPDATE test SET sort = sort + 1 WHERE obj = 1 AND sort >= 2 ORDER BY sort DESC;
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Query OK, 2 rows affected (0.02 sec)
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Rows matched: 2 Changed: 2 Warnings: 0
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mysql> INSERT INTO test (text, created, obj, sort) VALUES
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-> ('はじめまして', '2016-12-13', 1, 2);
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Query OK, 1 row affected (0.00 sec)
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mysql> COMMIT;
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Query OK, 0 rows affected (0.01 sec)
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mysql> SELECT * FROM test ORDER BY obj, sort;
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+----+--------------------------------------------+------------+-----+------+
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| id | text | created | obj | sort |
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+----+--------------------------------------------+------------+-----+------+
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| 1 | こんにちは | 2016-12-11 | 1 | 1 |
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| 7 | はじめまして | 2016-12-13 | 1 | 2 |
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| 2 | 私の名前は太郎です | 2016-12-12 | 1 | 3 |
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| 3 | どうぞよろしくお願いします。 | 2016-12-13 | 1 | 4 |
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| 4 | こんばんは | 2016-12-11 | 2 | 1 |
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| 5 | 私の名前は花子です | 2016-12-12 | 2 | 2 |
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| 6 | どうぞよろしくお願いします。 | 2016-12-13 | 2 | 3 |
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+----+--------------------------------------------+------------+-----+------+
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7 rows in set (0.00 sec)
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```
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