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I have a column (which represents an e-mail) in a SQL Server database with varchar(50) as data type and I would like to make it unique (do not allow the same two e-mail addresses). I cannot find a way to make such column unique in SQL Server Management Studio.
How to do that?
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In the Object Explorer under the table right-click the Indexes folder and choose New Index... . In the window that appears enter Index name: , tick the Unique checkbox and add your email field from the Add... button then click OK.
Varchar(50) stores a maximum of 50 characters. Varchar(max) stores a maximum of 2,147,483,647 characters. But, varchar(50) keeps the 50 character space even if you don't store 50 characters. but varchar(max) is flexible to any size.
Expand the "General" tab. Make sure you have the column you want to make unique selected in the "columns" box. Change the "Type" box to "Unique Key".
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.
In T-SQL it would be
ALTER TABLE MyTable WITH CHECK ADD CONSTRAINT UQ_MyTable_Email UNIQUE (EmailAddress) Or as an explicit index
CREATE UNIQUE INDEX IXU_Email ON MyTable (EmailAddress) Edit: I can't see how to create a constraint in the SSMS GUI: other answers show how to manage indexes. I do only use SQL though, never the GUI for this kind of work
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