MySQL 5.7.6のgenerated columnは関数インデックスの夢を見るか

MySQL 5.7.6-m16で導入されたgenerated columnについてメモ。タイトルでしゃらっと関数インデックスとか言っているけれど、俺はその機能を知らない。

MySQL :: MySQL 5.7 Reference Manual :: 13.1.14 CREATE TABLE Syntax

generated columnはあるカラムの値に関数を噛ませた結果をカラムとして実体化できたり、実体化せずに毎回計算できたりするカラム定義のことらしくて、

mysql57> CREATE TABLE t1 (num int PRIMARY KEY, val varchar(32)) Engine = MyISAM;
Query OK, 0 rows affected (0.01 sec)

mysql57> INSERT INTO t1 SET num = 1, val = 'one';
Query OK, 1 row affected (0.00 sec)

mysql57> SELECT * FROM t1;
+-----+------+
| num | val  |
+-----+------+
|   1 | one  |
+-----+------+
1 row in set (0.00 sec)

$ od -c t1.MYD
0000000 003  \0  \n 006  \0 376 001  \0  \0  \0 003   o   n   e  \0  \0
0000020  \0  \0  \0  \0
0000024

こんなテーブルに対して

mysql57> ALTER TABLE t1 ADD new_val varchar(96) AS (REPEAT(val, 3)) STORED KEY;
Query OK, 1 row affected (0.02 sec)
Records: 1  Duplicates: 0  Warnings: 0

"STORED"キーワードは演算結果を実体化してデータとして格納するオプション。STOREDオプションで作成されたgenerated columnにはインデックスを作成することができる。

mysql57> SELECT * FROM t1;
+-----+------+-----------+
| num | val  | new_val   |
+-----+------+-----------+
|   1 | one  | oneoneone |
+-----+------+-----------+
1 row in set (0.00 sec)

$ od -c t1.MYD
0000000 003  \0 024  \0  \0 374 001  \0  \0  \0 003   o   n   e  \t   o
0000020   n   e   o   n   e   o   n   e
0000030

$ od -c t1.MYI
..
*
0004000  \0 024  \0 001  \t   o   n   e   o   n   e   o   n   e  \0  \0
0004020  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0  \0
*
..

一応、インデックスとしても実体化されているぽい。

mysql57> INSERT INTO t1 SET num = 2, val = 'two';
Query OK, 1 row affected (0.00 sec)

mysql57> INSERT INTO t1 SET num = 3, val = 'three';
Query OK, 1 row affected (0.00 sec)

mysql57> explain SELECT * FROM t1 WHERE new_val LIKE 'one%';
+----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+-----------------------+
| id | select_type | table | partitions | type  | possible_keys | key     | key_len | ref  | rows | filtered | Extra                 |
+----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+-----------------------+
|  1 | SIMPLE      | t1    | NULL       | range | new_val       | new_val | 99      | NULL |    1 |   100.00 | Using index condition |
+----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+-----------------------+
1 row in set, 1 warning (0.00 sec)

mysql57> show warnings;
+-------+------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Level | Code | Message                                                                                                                                                         |
+-------+------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Note  | 1003 | /* select#1 */ select `d1`.`t1`.`num` AS `num`,`d1`.`t1`.`val` AS `val`,`d1`.`t1`.`new_val` AS `new_val` from `d1`.`t1` where (`d1`.`t1`.`new_val` like 'one%') |
+-------+------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

極めてフツーにカラムを作って、極めてフツーに値を突っ込んで、極めてフツーに検索しているのと同じ感じ（当たり前）

ただし、generated columnからフツーの(?)カラムに対する逆関数は定義できないので、

mysql57> INSERT INTO t1 SET num = 4, new_val = 'fourfourfour';
ERROR 3105 (HY000): The value specified for generated column 'new_val' in table 't1' is not allowed.

突っ込めない。
おお、噂（？）の3000番台エラーだ。


で、このgenerated columnでやりたいのって

mysql57> create table json (id int auto_increment, col1 varchar(1000), primary key(id));
Query OK, 0 rows affected (0.05 sec)

mysql57> INSERT INTO json(id, col1) VALUES (1, '{"id":1,"Name":"Farmer grandmas","price":50000,"Conditions":["farms",15]}');
Query OK, 1 row affected (0.00 sec)

mysql57> INSERT INTO json(id, col1) VALUES (2, '{"id":2,"Name":"Worker grandmas","price":300000,"Conditions":["factories",15]}');
Query OK, 1 row affected (0.00 sec)

mysql57> INSERT INTO json(id, col1) VALUES (3, '{"id":3,"Name":"Miner grandmas","price":1000000,"Conditions":["mines",15]}');
Query OK, 1 row affected (0.02 sec)

mysql57> INSERT INTO json(id, col1) VALUES (4, '{"id":4,"Name":"Yoshiaki Yamasaki"}');
Query OK, 1 row affected (0.01 sec)

mysql57> SELECT * FROM json;
+----+--------------------------------------------------------------------------------+-----------+
| id | col1                                                                           | gen_price |
+----+--------------------------------------------------------------------------------+-----------+
|  1 | {"id":1,"Name":"Farmer grandmas","price":50000,"Conditions":["farms",15]}      |     50000 |
|  2 | {"id":2,"Name":"Worker grandmas","price":300000,"Conditions":["factories",15]} |    300000 |
|  3 | {"id":3,"Name":"Miner grandmas","price":1000000,"Conditions":["mines",15]}     |   1000000 |
|  4 | {"id":4,"Name":"Yoshiaki Yamasaki"}                                            |      NULL |
+----+--------------------------------------------------------------------------------+-----------+
4 rows in set (0.00 sec)

mysql57> ALTER TABLE json ADD price int unsigned AS (json_extract(col1, 'price')) STORED;
Query OK, 4 rows affected (0.07 sec)
Records: 4  Duplicates: 0  Warnings: 0

mysql57> ALTER TABLE json ADD KEY (price);
Query OK, 0 rows affected (0.05 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql57> SELECT * FROM json WHERE price > 500000;
+----+----------------------------------------------------------------------------+---------+
| id | col1                                                                       | price   |
+----+----------------------------------------------------------------------------+---------+
|  3 | {"id":3,"Name":"Miner grandmas","price":1000000,"Conditions":["mines",15]} | 1000000 |
+----+----------------------------------------------------------------------------+---------+
1 row in set (0.00 sec)

こーゆーことで合ってますかね？ :)


( ´-｀).oO（サンプルのJSONは 日本語JSON UDFの一番詳しいスライドから拝借した


ところでADD price int unsigned AS (..) STORED KEYってやるとPRIMARYつけてなくてもPRIMARY KEYにしたがるんだけどたぶんバグだよな。。

【2015/03/23 19:44】
とりあえずばぐれぽしてみた。
MySQL Bugs: #76450: generated column with "KEY" makes PRIMARY KEY