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How do I make two columns unique in SQL?
Add SQL UNIQUE constraint using SQL ALTER TABLE statement. You can add a UNIQUE constraint to an existing table using ALTER TABLE statement. For example, the following query adds a UNIQUE constraint for two columns: username and email.
How do you make a table column unique?
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”. Click “Close”.
How do I add a unique column in SQL?
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);
Can you have a primary key with two columns?
Today I found out you can have a primary key using two columns (tsql). The PK must be unique but both columns do not (the combo must be unique). I thought that was very cool.
How to add unique constraint to combination of two columns?
I have a table and, somehow, the same person got into my Person table twice. Right now, the primary key is just an autonumber but there are two other fields that exist that I want to force to be unique. I only want 1 record with a unique PersonNumber and Active = 1.
What’s the difference between unique and primary key constraints?
The UNIQUE constraint ensures that all values in a column are different. Both the UNIQUE and PRIMARY KEY constraints provide a guarantee for uniqueness for a column or set of columns.
Can you have two primary keys in MySQL?
Today I found out you can have a primary key using two columns (tsql). The PK must be unique but both columns do not (the combo must be unique). I thought that was very cool. There were at least two SO question I asked where people yelled at me that I was doing my (mysql) databases wrong with only one person saying I did it fine.