An important Drizzle/MySQL difference

There are many features that are similar in MySQL and Drizzle. There are also many that are not.

I’ve previously discussed topics like Datatypes and tables, SQL_MODE and SHOW.

A key difference in Drizzle is the definition of utf8 as 4 bytes, not 3 bytes as in MySQL. This combined with no other character sets leads to an impact on the length in keys supported in Innodb.

During a recent test with a client, I was unable to successfully migrated the schema and provide the same schema due to unique indexes defined for utf8 VARHAR(255) fields.

Here is the problem.

mysql> create table t1(c1 int unsigned not null auto_increment primary key, c2 varchar(255) not null, unique key (c2)) engine=innodb default charset latin1;
Query OK, 0 rows affected (0.05 sec)
mysql> create table t2(c1 int unsigned not null auto_increment primary key, c2 varchar(255) not null, unique key (c2)) engine=innodb default charset utf8;
Query OK, 0 rows affected (0.03 sec)
mysql> create table t3(c1 int unsigned not null auto_increment primary key, c2 varchar(256) not null, unique key (c2)) engine=innodb default charset utf8;
ERROR 1071 (42000): Specified key was too long; max key length is 767 bytes
drizzle> create table t1(c1 int not null auto_increment primary key, c2 varchar(255) not null, unique key (c2)) engine=innodb default charset latin1;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your Drizzle server version for the right syntax to use near 'charset latin1' at line 1
drizzle> create table t1(c1 int not null auto_increment primary key, c2 varchar(255) not null, unique key (c2)) engine=innodb;
ERROR 1071 (42000): Specified key was too long; max key length is 767 bytes

Only a maximum of 191 is now possible.

drizzle> create table t1(c1 int not null auto_increment primary key, c2 varchar(191) not null, unique key (c2)) engine=innodb;
Query OK, 0 rows affected (0.03 sec)
drizzle> create table t1(c1 int not null auto_increment primary key, c2 varchar(192) not null, unique key (c2)) engine=innodb;
ERROR 1071 (42000): Specified key was too long; max key length is 767 bytes

Comments

  1. says

    Hi!

    You can always skip character sets and just use varbinary is you don’t need them. Adjusting up the size of the key is something we still need to do.

    Cheers,
    -Brian