J
jmls
Guest
"Nothing but the key" A memorable statement of Codd's definition of 3NF, paralleling the traditional pledge to give true evidence in a court of law, was given by Bill Kent: "[Every] non-key [attribute] must provide a fact about the key, the whole key, and nothing but the key." A common variation supplements this definition with the oath: "so help me Codd".[8] Requiring existence of "the key" ensures that the table is in 1NF; requiring that non-key attributes be dependent on "the whole key" ensures 2NF; further requiring that non-key attributes be dependent on "nothing but the key" ensures 3NF." http://en.wikipedia.org/wiki/Third_normal_form so if table A has id1 and id2 as a primary key, and tableB is linked to table A using id1 and id2 then table B is not TNF as it has duplicated items apart from the key attribute of A in other words, table A should have a unique key (guid) and table B should have an index with the first component of tableA_guid On 13 May 2014 13:58, ChUIMonster wrote: RE: composite foreign keys Reply by ChUIMonster In what way does a composite foreign key violate TNF? Stop receiving emails on this subject. Flag this post as spam/abuse. -- Julian Lyndon-Smith IT Director, dot.r http://www.dotr.com "The bitterness of poor quality remains long after the sweetness of low price is forgotten” Follow dot.r on http://twitter.com/DotRlimited
Continue reading...
Continue reading...