Database System - Basic SQL

View

A view is either a partial reference (i.e., not the whole table) to or a read-only view upon some table.

Updatable view and read-only view

If a view satisfy the following conditions, it’s updatable:

• Every row in the view can be uniquely mapped to a row in one table.
• Columns in the view should not be expression. (e.g. SELECT a.id + 1 FROM a;)

Create a view

CREATE VIEW <VIEW> [(<COLUMN1> <COLUMN2> ... <COLUMNn>)]
AS
<SELECT_QUERY>
[WITH CHECK OPTION]

• WITH CHECK OPTION ensures the view updates when its contents are updated by other queries.

See also CMU 15-445 (2025 Fall) Model SQL.