SQL Server - How to insert a record and make sure it is unique

Question

I\'m trying to figure out the best way to insert a record into a single table but only if the item doesn\'t already exist. The KEY in this case is an NVARCHAR(400) field. Fo

Answer 1

If you are using MS SQL Server, you can create a unique index on your table's columns that need to be unique (documented here):

CREATE UNIQUE [ CLUSTERED | NONCLUSTERED ] INDEX 
    ON Words ( word [ ASC | DESC ])

Specify Clustered or NonClustered, depending on your case. Also, if you want it sorted (to enable faster seeking), specify ASC or DESC for the sort order.

See here, if you want to learn more about indexes architecture.

Otherwise, you could use UNIQUE CONSTRAINTS like documented here:

ALTER TABLE Words
ADD CONSTRAINT UniqueWord
UNIQUE (Word);