Joe Celko's Thinking in Sets: Auxiliary, Temporal, and Virtual Tables in SQL

Chapter 6. Views

A VIEW IS a virtual table defined by a query that does not exist until it is invoked by name in an SQL statement. I will get into details about what the invocation can mean in physical terms shortly. The Standard SQL syntax for the VIEW definition is

CREATE VIEW <table name> [(<view column list>)]
AS <query expression>
[WITH [<levels clause>] CHECK OPTION]
<levels clause> ::= CASCADED | LOCAL

The <levels clause> option in the WITH CHECK OPTION did not exist in SQL-89 and it is still not widely implemented. This clause has no effect on queries, but only on UPDATE, INSERT, and DELETE statements. You cannot put constraints on a VIEW, as you can with base and TEMPORARY tables. A VIEW has no existence in the database until it is ...