I would like to see that produced on virgin tables. Primary Key does not allow nulls. Data row in FK table cannot be created unless data exists in PK table..
----- Original Message ----- From: "Anthony Schmidt" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Tuesday, April 09, 2002 12:28 PM Subject: Re: Please explain foreign keys, index - Razzak's Reply - correction regarding NULL status of Foreign Keys > Correction - > > A Foreign Key can be NULL. > > A trap for the unwary is that unless you select the NOT NULL constraint > when creating a Foreign Key, your Foreign Key will permit NULL values. > > This IS NOT an RBase bug because it conforms to the SQL standard. > > You can change the NOT NULL constraint for the Foreign Key after the fact. > > > > Tony > > Anthony J. Schmidt, JD > President > The Computery Ltd. > One East Main Street > Bay Shore, NY 11706 > > 631-665-8100 Voice > 631-969-5988 FAX > > http://www.computeryltd.com > > > > > > [EMAIL PROTECTED] > 04/09/2002 12:13 PM > Please respond to rbase-l > > > To: [EMAIL PROTECTED] > cc: (bcc: Anthony Schmidt/BayShore/SGU_LN) > Subject: Re: Please explain foreign keys, index - Razzak's Reply > > > > 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/ > > > > ================================================ > 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/ > ================================================ 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/
