Progress
Database Design
Guide


Keys

There are two types of keys: primary and foreign.

A primary key is a column (or group of columns) whose value uniquely identifies each row in a table. Because the key value is always unique, you can use it to detect and prevent duplicate rows. You can have only one primary key per table. Primary keys may be referenced by other tables. There can be only one primary key for a table. For more information on criteria for choosing a primary key refer to Introduction."

A foreign key is a column of data that is common to more than one table (and it is the primary key of one of these tables). It is this relationship of a column in one table to a column in another table that provides the relational database with its ability to join tables. "Table Relationships and Normalization," describes this concept in more detail.

When using SQL-92, you create your keys when you create your table. For information on the SQL CREATE TABLE command see the Progress SQL-92 Guide and Reference.


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