Explain what makes sql unique and how to identify it

Is this page helpful? Yes No. Any additional feedback? Skip Submit. Submit and view feedback for This product This page. View all page feedback. Create Unique Constraints. Modify Unique Constraints. Delete Unique Constraints. Describes how to disable a check constraint when a replication agent inserts or updates data in your table. Copy and paste the following example into the query window and select Execute. The example creates a unique constraint on the columns PasswordHash and PasswordSalt in the table Person.

The example creates a table and defines a unique constraint on the column TransactionID. Feedback will be sent to Microsoft: By pressing the submit button, your feedback will be used to improve Microsoft products and services.

Privacy policy. Exercise: Select all the different values from the Country column in the Customers table. Report Error. Your message has been sent to W3Schools. W3Schools is optimized for learning and training. Good question!

ID analytics maintains in that 20 million Americans have multiple social security number associated with their name. Do you want your primary key to rely on government data? Now that you know the differences, and see there are also a lot of similarities between primary and unique key, you may have question when to use each. Let me answer those:. In my book, every table should have a primary key. It provides the main way primary to identify each row. This becomes a great way to ensure data validation.

In our example, we used the GovernmentNumber, but many others occur. In fact, you often see a pattern with the primary key is a synthetic value such as an identity value sequence , therefore, an naturally occurring unique values, such as Account Numbers become candidates for unique keys.