How add primary key constraint to existing column in SQL Server?

How add primary key constraint to existing column in SQL Server?

Using SQL Server Management Studio

1. In Object Explorer, right-click the table to which you want to add a unique constraint, and click Design.
2. In Table Designer, click the row selector for the database column you want to define as the primary key.
3. Right-click the row selector for the column and select Set Primary Key.

How do I add a foreign key to an existing SQL table?

Using SQL Server Management Studio

1. In Object Explorer, right-click the table that will be on the foreign-key side of the relationship and click Design.
2. From the Table Designer menu, click Relationships.
3. In the Foreign-key Relationships dialog box, click Add.
4. Click the relationship in the Selected Relationship list.

How to create a primary key constraint in SQL?

To create a PRIMARY KEY constraint on the “ID” column when the table is already created, use the following SQL: To allow naming of a PRIMARY KEY constraint, and for defining a PRIMARY KEY constraint on multiple columns, use the following SQL syntax:

How to add a primary key to an existing table?

How to Add a Primary Key to an Existing Table in SQL Server (T-SQL Examples) Example 1 – Add a Primary Key Constraint Example 2 – Check the Primary Key Constraint Example 3 – Adding a Primary Key to a Column that allows NULL Values Example 4 – Altering a Column to be an Identity Column

Can a primary key have more than one column?

If a primary key consists of more than one column, duplicate values are allowed in one column, but each combination of values from all the columns in the primary key must be unique.

Can a primary key be added to a column that is not null?

A primary key can only be added to columns that are defined as NOT NULL. If you try to add a primary key to a column that is nullable, you’ll get an error. To demonstrate this, let’s create another table, but this time, we’ll also forget to specify the column as NOT NULL: