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SQL database views are in effect virtual tables. They can be queried in the same way as a table but they do not store data. The data that appears to be stored in a view is in fact defined by a stored query applied to the data stored in one or more tables.

It is important to be aware of performance issues related to the use of database views. For example, views that refer to other views can result in queries that take longer to process. Although, a detailed discussion on this topic is outside the scope of this guide, please keep this in mind when using the views and composite views that were created as part of this SNOMED CT example MySQL database.

The SNOMED CT import process creates two distinct types of views. Filtered views of a single table and composite views that bring together related data from different tables.

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