I have found a "problem" with UNIQUE in InnoDB.
Example:
mysql> CREATE TABLE b (
-> idB int(11) NOT NULL auto_increment,
-> valor int(11) default NULL,
-> PRIMARY KEY (idB),
-> UNIQUE KEY valor (valor)
-> ) TYPE=MyISAM;
Query OK, 0 rows affected (0.00 sec)
mysql> INSERT INTO b (idB, valor) VALUES (1,1),(2,2),(3,NULL),(4,NULL);
Query OK, 4 rows affected (0.01 sec)
Registros: 4 Duplicados: 0 Peligros: 0
mysql> select * from b;
+-----+-------+
| idB | valor |
+-----+-------+
| 1 | 1 |
| 2 | 2 |
| 3 | NULL |
| 4 | NULL |
+-----+-------+
4 rows in set (0.00 sec)
mysql> alter table b type=InnoDB;
ERROR 1062: Entrada duplicada 'NULL' para la clave 2
Why? I know that NULL != NULL, then behaviour in MyISAM is correct but
in InnoDB in not.
With "foreign key constraints", I have found the same problem: I can't
insert a NULL in a column that "references" other.
Thanks,
José Ceferino Ortega
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