Using NULL values for Foreign Keys

• Trystan Hughes

  SSCrazy

  Points: 2109

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  April 11, 2006 at 2:56 pm

  #111745

  Hi all, I have a table, Issues, that also has a column named 'CauseUID' that is a Foreign key to the 'Causes' table. It is not always possible/known what the cause is to an Issue in the 'Issues' table, so for rows in the 'Issues' table that don't have a cause 'CauseUID', do I put a NULL value in this column, or a a '0' value?

  Thanks

  Tryst

• Antares686

  SSC Guru

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  April 11, 2006 at 3:00 pm

  #631961

  Best bet is Null. With 0 you are just creating a substituion which could in theory become valid at some point.

• Sergiy

  SSC Guru

  Points: 110208

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  April 11, 2006 at 5:21 pm

  #631981

  NULL is not better, it's ONLY RIGHT option.

  To use '0' instead of NULL you need either drop FK constraint or create dummy record with ID = '0' in 'Causes' table.

  Both options are not acceptable for so many reasons it may take too much time to list them here and than read it.

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