syntax for making the column as unique

Hi,
I need help in finding out the syntax for adding unique constrant on the column. I have one column called username, which is NOT NULL already, but I also want this column to be unique(no duplicate). I could not find syntax which is working. Thanks for help.

Dragon

you can either create a Primary Key constraint on this column (which will create a unique index as well) or just create a unique index on this column.

- Rajeev

ALTER TABLE your_table
ADD CONSTRAINT your_unique_constraint UNIQUE (your_unique_column)

Thanks.

so a primary key consists on a unique key and a not null constraint

Quote:

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Originally posted by tomate
so a primary key consists on a unique key and a not null constraint

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It used to be like this, but not any more. Now you can have a primary key constraint built on a non-unique index. But of course, the indexed values still need to be unique in order the PK constraint to be enforced.