A primary key is a column or combination of columns that uniquely identifies a row. It cannot be NULL and it must have a unique index. A table with a primary key is eligible for joins with foreign keys in other tables. The primary key table can be thought of as the master table in a master-detail relationship. There can be many such master-detail groups in a database.
In the pubs2 database, for example, the title_id column is the primary key of titles. It uniquely identifies the books in titles, and joins with title_id in titleauthor, salesdetail, and roysched. The titles table is the master table in relation to titleauthor, salesdetail, and roysched. For more information about pubs2, see the Adaptive Server Enterprise Reference Manual.
Specifying a primary key on a column
Open the Table Editor
Select the column you want.
Click the icon under the title Key.
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