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How do I create a unique constraint on an existing table in SQL Server 2005?
I am looking for both the TSQL and how to do it in the Database Diagram.
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To create a unique constraintOn the Table Designer menu, select Indexes/Keys. In the Indexes/Keys dialog box, select Add. In the grid under General, select Type and choose Unique Key from the drop-down list box to the right of the property, and then select Close.
The syntax for creating a unique constraint using an ALTER TABLE statement in SQL Server is: ALTER TABLE table_name ADD CONSTRAINT constraint_name UNIQUE (column1, column2, ... column_n); table_name.
SQL UNIQUE constraint for 2 columns example Notice that we named the UNIQUE constraints using CONSTRAINT keyword. We can use this name to remove the UNIQUE constraint later if we want. To define a UNIQUE on multiple columns, we put a comma-separated columns list inside parenthesis that follows the UNIQUE keyword.
To define a UNIQUE constraint, you use the UNIQUE keyword followed by one or more columns. You can define a UNIQUE constraint at the column or the table level. Only at the table level, you can define a UNIQUE constraint across multiple columns.
The SQL command is:
ALTER TABLE <tablename> ADD CONSTRAINT <constraintname> UNIQUE NONCLUSTERED ( <columnname> ) See the full syntax here.
If you want to do it from a Database Diagram:
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