Not every DBMS... MSSQL: Create Unique Index Microsoft(r) SQL Server(tm) checks for duplicate values when the index is created (if data already exists) and checks each time data is added with an INSERT or UPDATE statement. If duplicate key values exist, the CREATE INDEX statement is canceled and an error message giving the first duplicate is returned. Multiple NULL values are considered duplicates when UNIQUE index is created.
SYBASE: Create Unique Index Prohibits duplicate index (also called key) values. The system checks for duplicate key values when the index is created (if data already exists), and checks each time data is added with an insert or update. If there is a duplicate key value or if more than one row contains a null value, the command is aborted and an error message giving the duplicate is printed. Ed -----Original Message----- From: Jay Blanchard [mailto:[EMAIL PROTECTED] Sent: Tuesday, April 26, 2005 6:50 AM To: Jigal van Hemert; mysql@lists.mysql.com Subject: RE: why NOT NULL in PRIMARY key?? Since NULL is the absence of a value and PRIMARY keys must have a value a NULL column cannot be included as a portion of a PRIMARY key. AFAIK this is the case with every RDBMS out there. Asking the development team might get you a more informative response. There is a vast difference between a zero value, blank value and NULL (absence of value). -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/[EMAIL PROTECTED] -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/[EMAIL PROTECTED]
