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From:Gaspar Bakos Date:December 28 2004 10:18pm
Subject:Re: unique key <-> primary key
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Hi,

RE:
> And columns in primary keys must be NOT NULL.  Columns in unique
> keys can be NULL (if they are NOT NULL, then the unique key is
> functionally the same as a primary key).

OK, thanks guys for the explanation.

Then the result of mysqldump table definition part:

UNIQUE KEY HONstid (HONstid,HONname)

means that I have two unique keys:
HONstid
and also the
(HONstid,HONname) combination?

This does not make too much sense; if I can have only one HONstid in my
table, then of course i can have only one kind of (HONstid,HONname)
combination. In the actual table, I have multiple occurences of values
(HONstid,HONname)in the HONstid column, i.e. it does not seem like
HONstid in itself was a unique key. Only the (HONstid,HONname)
combination is unique.

Cheers
Gaspar

p.s.: Paul, I very much enjoy your MySQL book.
Thread
unique key <-> primary keyGaspar Bakos28 Dec
  • Re: unique key <-> primary keyMartijn Tonies28 Dec
    • Re: unique key <-> primary keyPaul DuBois28 Dec
      • Re: unique key <-> primary keyGaspar Bakos28 Dec
  • Re: unique key <-> primary keyMartijn Tonies29 Dec
  • Re: unique key <-> primary keyMartijn Tonies29 Dec