constraint expression for unique keys

[HandersonVA]

if i have a table which defines a rule as "combinatio n of two field
must be unique", how can I write this in a constraint expression
section?
i started learning more about ms sql side to handle all the necessary
rules in back-end instead of front-end.
also any good learning links, references, or book recommandations ?
thanks

[Alexander Kuznetsov]

Re: constraint expression for unique keys

an excerpt from BOL:

"C. Using UNIQUE constraints
UNIQUE constraints are used to enforce uniqueness on nonprimary key
columns. The following example enforces a restriction that the Name
column of the Product table must be unique.

Copy Code
Name nvarchar(100) NOT NULL
UNIQUE NONCLUSTERED

"

[HandersonVA]

Re: constraint expression for unique keys

can you explain what "NONCLUSTER ED" is doing there? is that for
non-relation to a field in other table?

Alexander Kuznetsov wrote:[color=blue]
> an excerpt from BOL:
>
> "C. Using UNIQUE constraints
> UNIQUE constraints are used to enforce uniqueness on nonprimary key
> columns. The following example enforces a restriction that the Name
> column of the Product table must be unique.
>
> Copy Code
> Name nvarchar(100) NOT NULL
> UNIQUE NONCLUSTERED
>
> "[/color]

[Alexander Kuznetsov]

Re: constraint expression for unique keys

SQL Server implicitly creates an index to implement a uinque
constraint. In this case NONCLUSTERED means the index will be
non-clustered.

[Erland Sommarskog]

Re: constraint expression for unique keys

HandersonVA (handersonva@ho tmail.com) writes:[color=blue]
> if i have a table which defines a rule as "combinatio n of two field
> must be unique", how can I write this in a constraint expression
> section?[/color]

CONSTRAINT u_tbl UNIQUE (col1, col2)




--
Erland Sommarskog, SQL Server MVP, esquel@sommarsk og.se

Books Online for SQL Server 2005 at

http://www.microsoft.com/technet/prodtechnol/sql/2005/downloads/books.mspx

Books Online for SQL Server 2000 at

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[--CELKO--]

Re: constraint expression for unique keys

>> if i have a table which defines a rule as "combinatio n of two field must be unique", how can I write this in a constraint expression section? <<

CONSTRAINT unique_location UNIQUE (x, y)[color=blue][color=green]
>> any good learning links, references, or book recommandations ? <<[/color][/color]

I recommend buying all of my books :)