TL;DR
- MySQL 5.7とそれ以前では
ALTER TABLE t1 CHANGE a b int ..とかやらないといけなかったのが、 ALTER TABLE t1 RENAME COLUMN a TO bでデータ型とか気にせずにいけるようになっていた - 地味にうれしい
- 参考資料
今まではこう
mysql57 40> CREATE TABLE t1 (num int unsigned not null, val varchar(32) not null, PRIMARY KEY(num), FULLTEXT KEY (val) WITH PARSER ngram);
Query OK, 0 rows affected (0.06 sec)
mysql57 40> SHOW CREATE TABLE t1\G
*************************** 1. row ***************************
Table: t1
Create Table: CREATE TABLE `t1` (
`num` int(10) unsigned NOT NULL,
`val` varchar(32) NOT NULL,
PRIMARY KEY (`num`),
FULLTEXT KEY `val` (`val`) /*!50100 WITH PARSER `ngram` */
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4
1 row in set (0.00 sec)
mysql57 40> ALTER TABLE t1 CHANGE val abc varchar(32) NOT NULL;
Query OK, 0 rows affected (0.01 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql57 40> SHOW CREATE TABLE t1\G
*************************** 1. row ***************************
Table: t1
Create Table: CREATE TABLE `t1` (
`num` int(10) unsigned NOT NULL,
`abc` varchar(32) NOT NULL,
PRIMARY KEY (`num`),
FULLTEXT KEY `val` (`abc`) /*!50100 WITH PARSER `ngram` */
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4
1 row in set (0.01 sec)
CHANGEの後にデータ型もつけなければいけなかったのが面倒だった。 NOT NULLをつけるのを忘れて死にかけたりした人も世の中には存在するんじゃなかろうか。
これがMySQL 8.0ではこうじゃ。
mysql80 24> CREATE TABLE t1 (num int unsigned not null, val varchar(32) not null, PRIMARY KEY(num), FULLTEXT KEY (val) WITH PARSER ngram);
Query OK, 0 rows affected (0.15 sec)
mysql80 24> SHOW CREATE TABLE t1\G
*************************** 1. row ***************************
Table: t1
Create Table: CREATE TABLE `t1` (
`num` int(10) unsigned NOT NULL,
`val` varchar(32) COLLATE utf8mb4_ja_0900_as_cs NOT NULL,
PRIMARY KEY (`num`),
FULLTEXT KEY `val` (`val`) /*!50100 WITH PARSER `ngram` */
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_ja_0900_as_cs
1 row in set (0.00 sec)
mysql80 24> ALTER TABLE t1 RENAME COLUMN val TO abc;
Query OK, 0 rows affected (0.04 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql80 24> SHOW CREATE TABLE t1\G
*************************** 1. row ***************************
Table: t1
Create Table: CREATE TABLE `t1` (
`num` int(10) unsigned NOT NULL,
`abc` varchar(32) COLLATE utf8mb4_ja_0900_as_cs NOT NULL,
PRIMARY KEY (`num`),
FULLTEXT KEY `val` (`abc`) /*!50100 WITH PARSER `ngram` */
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_ja_0900_as_cs
1 row in set (0.00 sec)
ただし、generated columnがあると古い方のカラムを参照し続けるため ALTER TABLEが転ける。これは CHANGEでも転けるんだけれども。
mysql80 24> ALTER TABLE t1 ADD v_abc varchar(32) AS (MD5(abc)) NOT NULL;
Query OK, 0 rows affected (0.05 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql80 24> SHOW CREATE TABLE t1\G
*************************** 1. row ***************************
Table: t1
Create Table: CREATE TABLE `t1` (
`num` int(10) unsigned NOT NULL,
`abc` varchar(32) COLLATE utf8mb4_ja_0900_as_cs NOT NULL,
`v_abc` varchar(32) COLLATE utf8mb4_ja_0900_as_cs GENERATED ALWAYS AS (md5(`abc`)) VIRTUAL NOT NULL,
PRIMARY KEY (`num`),
FULLTEXT KEY `val` (`abc`) /*!50100 WITH PARSER `ngram` */
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_ja_0900_as_cs
1 row in set (0.00 sec)
mysql80 24> ALTER TABLE t1 RENAME COLUMN abc TO def;
ERROR 1054 (42S22): Unknown column 'abc' in 'generated column function'
mysql80 24> ALTER TABLE t1 CHANGE abc def varchar(32) NOT NULL;
ERROR 1054 (42S22): Unknown column 'abc' in 'generated column function'
綺麗に転けるならまだしも、 RENAME TABLEでたまにやるみたいにカラムをスワップさせようと思うと大変なことになる。
mysql80 24> SHOW CREATE TABLE t1\G
*************************** 1. row ***************************
Table: t1
Create Table: CREATE TABLE `t1` (
`num` int(10) unsigned NOT NULL,
`abc` varchar(32) COLLATE utf8mb4_ja_0900_as_cs NOT NULL,
`v_abc` varchar(32) COLLATE utf8mb4_ja_0900_as_cs GENERATED ALWAYS AS (md5(`abc`)) VIRTUAL NOT NULL,
`def` varchar(32) COLLATE utf8mb4_ja_0900_as_cs DEFAULT NULL,
PRIMARY KEY (`num`),
FULLTEXT KEY `val` (`abc`) /*!50100 WITH PARSER `ngram` */
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_ja_0900_as_cs
1 row in set (0.00 sec)
mysql80 24> SELECT * FROM t1;
+-----+-----+----------------------------------+------+
| num | abc | v_abc | def |
+-----+-----+----------------------------------+------+
| 1 | one | f97c5d29941bfb1b2fdab0874906ab82 | NULL |
+-----+-----+----------------------------------+------+
1 row in set (0.00 sec)
mysql80 24> ALTER TABLE t1 RENAME COLUMN abc TO def, RENAME COLUMN def TO abc;
Query OK, 0 rows affected (0.08 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql80 24> SHOW CREATE TABLE t1\G
*************************** 1. row ***************************
Table: t1
Create Table: CREATE TABLE `t1` (
`num` int(10) unsigned NOT NULL,
`def` varchar(32) COLLATE utf8mb4_ja_0900_as_cs NOT NULL,
`v_abc` varchar(32) COLLATE utf8mb4_ja_0900_as_cs GENERATED ALWAYS AS (md5(`abc`)) VIRTUAL NOT NULL,
`abc` varchar(32) COLLATE utf8mb4_ja_0900_as_cs DEFAULT NULL,
PRIMARY KEY (`num`),
FULLTEXT KEY `val` (`def`) /*!50100 WITH PARSER `ngram` */
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_ja_0900_as_cs
1 row in set (0.00 sec)
mysql80 24> SELECT * FROM t1;
+-----+-----+-------+------+
| num | def | v_abc | abc |
+-----+-----+-------+------+
| 1 | one | | NULL |
+-----+-----+-------+------+
1 row in set (0.01 sec)
VIRTUAL generated columnはビューとかストアドと一緒で名前でしか参照されないので、「カラムが存在しない」以外ではエラーにならなさげ。
…あれ？ これSTOREDだとどうなるんだ？
mysql80 24> SHOW CREATE TABLE t1\G
*************************** 1. row ***************************
Table: t1
Create Table: CREATE TABLE `t1` (
`num` int(10) unsigned NOT NULL,
`abc` varchar(32) COLLATE utf8mb4_ja_0900_as_cs NOT NULL,
`def` varchar(32) COLLATE utf8mb4_ja_0900_as_cs DEFAULT NULL,
`v_abc` varchar(32) COLLATE utf8mb4_ja_0900_as_cs GENERATED ALWAYS AS (md5(`abc`)) STORED,
PRIMARY KEY (`num`),
FULLTEXT KEY `val` (`abc`) /*!50100 WITH PARSER `ngram` */
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_ja_0900_as_cs
1 row in set (0.00 sec)
mysql80 24> SELECT * FROM t1;
+-----+-----+------+----------------------------------+
| num | abc | def | v_abc |
+-----+-----+------+----------------------------------+
| 1 | one | NULL | f97c5d29941bfb1b2fdab0874906ab82 |
+-----+-----+------+----------------------------------+
1 row in set (0.00 sec)
mysql80 24> ALTER TABLE t1 RENAME COLUMN abc TO def, RENAME COLUMN def TO abc;
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql80 24> SHOW CREATE TABLE t1\G
*************************** 1. row ***************************
Table: t1
Create Table: CREATE TABLE `t1` (
`num` int(10) unsigned NOT NULL,
`def` varchar(32) COLLATE utf8mb4_ja_0900_as_cs NOT NULL,
`abc` varchar(32) COLLATE utf8mb4_ja_0900_as_cs DEFAULT NULL,
`v_abc` varchar(32) COLLATE utf8mb4_ja_0900_as_cs GENERATED ALWAYS AS (md5(`abc`)) STORED,
PRIMARY KEY (`num`),
FULLTEXT KEY `val` (`def`) /*!50100 WITH PARSER `ngram` */
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_ja_0900_as_cs
1 row in set (0.00 sec)
mysql80 24> SELECT * FROM t1;
+-----+-----+------+----------------------------------+
| num | def | abc | v_abc |
+-----+-----+------+----------------------------------+
| 1 | one | NULL | f97c5d29941bfb1b2fdab0874906ab82 |
+-----+-----+------+----------------------------------+
1 row in set (0.00 sec)
アッー！
ワークアラウンド: OPTIMIZE TABLEしたら再計算されたようで直った
mysql80 24> OPTIMIZE TABLE t1;
+-------+----------+----------+-------------------------------------------------------------------+
| Table | Op | Msg_type | Msg_text |
+-------+----------+----------+-------------------------------------------------------------------+
| d1.t1 | optimize | note | Table does not support optimize, doing recreate + analyze instead |
| d1.t1 | optimize | status | OK |
+-------+----------+----------+-------------------------------------------------------------------+
2 rows in set (0.18 sec)
mysql80 24> SELECT * FROM t1;
+-----+-----+------+-------+
| num | def | abc | v_abc |
+-----+-----+------+-------+
| 1 | one | NULL | NULL |
+-----+-----+------+-------+
1 row in set (0.00 sec)