CREATE VIEW

Defines a new view.

Synopsis

  1. CREATE [OR REPLACE] [TEMP | TEMPORARY] VIEW <name>
  2.        [ ( <column_name> [, ...] ) ]
  3.        AS <query>

Description

CREATE VIEW defines a view of a query. The view is not physically materialized. Instead, the query is run every time the view is referenced in a query.

CREATE OR REPLACE VIEW is similar, but if a view of the same name already exists, it is replaced. You can only replace a view with a new query that generates the identical set of columns (same column names and data types).

If a schema name is given then the view is created in the specified schema. Otherwise it is created in the current schema. Temporary views exist in a special schema, so a schema name may not be given when creating a temporary view. The name of the view must be distinct from the name of any other view, table, sequence, or index in the same schema.

Parameters

TEMPORARY | TEMP

If specified, the view is created as a temporary view. Temporary views are automatically dropped at the end of the current session. Existing permanent relations with the same name are not visible to the current session while the temporary view exists, unless they are referenced with schema-qualified names. If any of the tables referenced by the view are temporary, the view is created as a temporary view (whether TEMPORARY is specified or not).

The name (optionally schema-qualified) of a view to be created.

An optional list of names to be used for columns of the view. If not given, the column names are deduced from the query.

A SELECT command which will provide the columns and rows of the view.

Notes

Views in HAWQ are read only. The system will not allow an insert, update, or delete on a view. You can get the effect of an updatable view by creating rewrite rules on the view into appropriate actions on other tables. For more information see CREATE RULE.

Be careful that the names and data types of the view’s columns will be assigned the way you want. For example, if you run the following command:

  1. CREATE VIEW vista AS SELECT 'Hello World';

The result is poor: the column name defaults to ?column?, and the column data type defaults to unknown. If you want a string literal in a view’s result, use the following command:

  1. CREATE VIEW vista AS SELECT text 'Hello World' AS hello;

Check that you have permission to access the tables referenced in the view. View ownership determines permissions, not your status as current user. This is true, even if you are a superuser. This concept is unusual, since superusers typically have access to all objects. In the case of views, even superusers must be explicitly granted access to tables referenced if they do not own the view.

However, functions called in the view are treated the same as if they had been called directly from the query using the view. Therefore the user of a view must have permissions to call any functions used by the view.

If you create a view with an ORDER BY clause, the ORDER BY clause is ignored when you do a SELECT from the view.

Examples

Create a view consisting of all comedy films:

  1. CREATE VIEW comedies AS SELECT * FROM films WHERE kind = 
  2. 'comedy';

Create a view that gets the top ten ranked baby names:

  1. CREATE VIEW topten AS SELECT name, rank, gender, year FROM 
  2. names, rank WHERE rank < '11' AND names.id=rank.id;

Compatibility

The SQL standard specifies some additional capabilities for the CREATE VIEW statement that are not in HAWQ. The optional clauses for the full SQL command in the standard are:

  • CHECK OPTION — This option has to do with updatable views. All INSERT commands on the view will be checked to ensure data satisfy the view-defining condition (that is, the new data would be visible through the view). If they do not, the insert will be rejected.
  • LOCAL — Check for integrity on this view.
  • CASCADED — Check for integrity on this view and on any dependent view. CASCADED is assumed if neither CASCADED nor LOCAL is specified.

CREATE OR REPLACE VIEW is a HAWQ language extension. So is the concept of a temporary view.

See Also

SELECT, DROP VIEW