What makes sql unique

For more practice with table creation and database design, check out our track on Creating Database Structure. It includes basics of table creation, SQL data types, constraints, and more. And for some insight into the track, read this article. But what are the actual differences between them? The UNIQUE keyword marks a database constraint and is defined during table creation or later on a specific column or a set of columns. It directly follows the SELECT keyword when we want to make sure that all the rows of the result set contain distinct values or a distinct set of values.

Back to articles list Articles Cookbook. The primary key provides a means to identity the row, using data within the row. A primary key can be based on one or more columns, such as first and last name; however, in many designs, the primary key is an auto-generated number from an identity column.

All relational database management systems support primary keys. It is a fundamental concept. A database table is truly considered relational and in the first normal form once a primary key is defined. As you can see, the primary key is the main key of the table. Its main purpose is to identify each row. Another name for a unique key is unique constraint.

To ensure rows are unique within a database, use a unique constraint. Makes sense, but wait! Yep, we do, but a table may have several sets of columns which you want unique. Assuming that EmployeeID is the primary key, then we may want to place a unique constraint on GovernmentNumber to ensure each employee has their own number. A primary key main job is to uniquely identify a row within a table.

The fancy name for this is entity integrity. Skip to main content. This browser is no longer supported. Download Microsoft Edge More info. Contents Exit focus mode. Is this page helpful? Yes No. Any additional feedback?