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I have an existing table with data. I have just added a new column but I cannot find how to add a unique constraint on that column. Could someone please advise? Right-clicking and selecting "check constraints" wasn't helpful.
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Set column as unique in SQL Server from the GUI:Open SQL Server Management Studio. Right click your Table, click "Design". Right click the column you want to edit, a popup menu appears, click Indexes/Keys. Click the "Add" Button.
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.
The syntax for creating a unique constraint using an ALTER TABLE statement in MySQL is: ALTER TABLE table_name ADD CONSTRAINT constraint_name UNIQUE (column1, column2, ... column_n); table_name.
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.
You need to right-click in the table designer and pick Indexes/Keys:
Then a dialog pops up and you can add a new index to the list of indices (on the left hand side) and define it to be a unique index:
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