[hibernate-issues] [Hibernate-JIRA] Commented: (HHH-2235) Support for null map-keys in <map> mappings

[ http://opensource.atlassian.com/projects/hibernate/browse/HHH-2235?page=c... ] Christian Bauer commented on HHH-2235: -------------------------------------- Sure, most SQL DBMSs have broken NULL handling. When you INSERT a row, you might avoid duplicates in Oracle because they treat NULL as some special value (they have other crazy ideas about NULL, too). But NULL is not a value, you not compare two NULLs and get a true/false answer, hence, you can not determine uniqueness. So other DBMSs allow nullable columns in composite unique constraints but just ignore NULLs during INSERT check (MySQL I think). In DBMSs it only works as long as there is only a single row with a NULL value (SQL Server)! You will get duplicate rows and that is exactly the reason why the SQL guys came up with the notion of "primary key", which means a unique key that has no nullable components. (That is, a "candidate key" as defined by the relational data model. There are no NULLs in the relational data model.) -- This message is automatically generated by JIRA. - If you think it was sent incorrectly contact one of the administrators: http://opensource.atlassian.com/projects/hibernate/secure/Administrators.... - For more information on JIRA, see: http://www.atlassian.com/software/jira