List:General Discussion« Previous MessageNext Message »
From:Paul DuBois Date:June 13 1999 10:34pm
Subject:Re: primary and unique indexes
View as plain text  
At 5:25 PM -0500 6/13/1999, Tim Winders wrote:
>On Sun, 13 Jun 1999, Paul DuBois wrote:
>
>> At 9:22 PM +0300 6/13/1999, Mark Papadakis wrote:
>> >Hi!
>> >
>> >Is a primary index exactly the same thing as a unique index, except that it
>> >is market as a primary?
>>
>> They are the same.
>>
>> >Also, do primary/unique keys make sense only on multi-column keys?
>>
>> What does that mean, "make sense"?  Do you mean "are they only useful
>> for multi-column keys"?  If so, the answer is no.  For example, any table
>> which lists unique entities and has an identifier number column will
>> likely benefit from putting a unique index on that column.
>
>But, multi-column unique indexes DO make sense in some cases.  For
>example.  I have a jobs database with a Prospects table.  The only columns
>in the table are JobID and ProspectID.  Neither column can be unique,
>(each Job can have multiple Prospects and each prospect could be
>candidates for multiple jobs) but the combination of both columns should
>be unique (the same person shouldn't be listed more than 1 time for each
>job).

Sure.  But I thought the question was whether they *only* make sense
for multi-column keys.

--
Paul DuBois, paul@stripped
Northern League Chronicles: http://www.snake.net/nl/
Thread
primary and unique indexesMark Papadakis13 Jun
  • Re: primary and unique indexesPaul DuBois14 Jun
    • Re: primary and unique indexesTim Winders14 Jun
      • Re: primary and unique indexesPaul DuBois14 Jun