At 04:00 PM 4/7/2002 -0400, Bernie Lis wrote:
>what is diff between foreign key and foreign index? >If I create a foreign index is that column indexed for >look ups in that table. If I create a foreign key do I >still have to build an index for look up in that table? Bernie, TTBOMK there is no such thing as Foreign Index. . An Index is automatically built when a foreign key constraint is defined. . Key is a column or set of columns that identify a row. . All other columns should be dependent on a key. . A key is NOT an index. . A key is often indexed, but these terms are not interchangeable. . Primary Key is a column or set of columns that uniquely identify a row. . Foreign Key is a column or set of columns that link to a Primary Key. . A Foreign Key matches a defined Primary Key, i.e, the value in a Foreign Key reference values in the Primary Key. . A Foreign Key can have duplicate values but cannot have NULLs. . The value in a Foreign Key must exist in a Primary Key and Primary Key also prohibits NULLs. . A Foreign Key replaces a verify a value rule. . Primary and Foreign Keys must match in terms of the specified number of columns. If you have a multi-column Primary Key, you cannot have single column Foreign Keys reference it. If you have a multi-column Foreign Key, it cannot reference a single Primary Key. When a Primary Key is defined as more than one column, those columns are treated as a whole. Primary and Foreign keys must much exactly. Examples (CONCOMP Database): . EmpID is the Primary Key for the Employee table. . EmpID is a Foreign Key in TransMaster table. It relates to the Primary Key in the Employee table. Hope that helps! Very Best Regards, Razzak. ================================================ TO SEE MESSAGE POSTING GUIDELINES: Send a plain text email to [EMAIL PROTECTED] In the message body, put just two words: INTRO rbase-l ================================================ TO UNSUBSCRIBE: send a plain text email to [EMAIL PROTECTED] In the message body, put just two words: UNSUBSCRIBE rbase-l ================================================ TO SEARCH ARCHIVES: http://www.mail-archive.com/rbase-l%40sonetmail.com/
