March 1, 2011 at 11:23 am
1. Can a column be set to not null, unique and primary?
2. Can a column be set to not null and unique?
3. Can a column be set to not null and primary?
4. Can a column be set to unique and primary?
:unsure:
March 1, 2011 at 11:26 am
Sounds a lot like homework to me. What have you tried, what do you think and where are having having troubles validating your assumptions?
March 1, 2011 at 11:51 am
Answering it myself...;-)
Tried on SQL Server 2008 management studio:
and it turns out answer for all Ques is Yes!!
...even though it is useless to set not null and/or unique when the column is declared a primary key!!
March 1, 2011 at 12:35 pm
Hmmm...this is strange !!
1. create table temp6 (id int unique primary key)
shows error: Both a PRIMARY KEY and UNIQUE constraint have been defined for column 'id', table 'temp6'. Only one is allowed.
2. create table temp6 (id int unique ,primary key(id))
Works!! LOL
March 1, 2011 at 3:49 pm
a unique primary key is like saying the white white rabbit. It's redundant and the code parser is likely picking this up.
However you ARE allowed to have 2 unique constraint, identical in every way except for their name. Of course it makes no logical sense to do it but it's allowed.
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