Defines a new view.
CREATE [OR REPLACE] [TEMP | TEMPORARY] VIEW <name>
[ ( <column_name> [, ...] ) ]
AS <query>
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.
TEMPORARY
is specified or not).
Views in Greenplum Database 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:
CREATE VIEW vista AS SELECT 'Hello World';
is bad form in two ways: 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 something like:
CREATE VIEW vista AS SELECT text 'Hello World' AS hello;
Access to tables referenced in the view is determined by permissions of the view owner not the current user (even if the current user is a superuser). This can be confusing in the case of superusers, since superusers typically have access to all objects. In the case of a view, even superusers must be explicitly granted access to tables referenced in the view if they are not the owner of 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.
Create a view consisting of all comedy films:
CREATE VIEW comedies AS SELECT * FROM films WHERE kind =
'comedy';
Create a view that gets the top ten ranked baby names:
CREATE VIEW topten AS SELECT name, rank, gender, year FROM
names, rank WHERE rank < '11' AND names.id=rank.id;
The SQL standard specifies some additional capabilities for the CREATE VIEW
statement that are not in Greenplum Database. The optional clauses for the full SQL command in the standard are:
INSERT
and UPDATE
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 update will be rejected.CASCADED
is assumed if neither CASCADED
nor LOCAL
is specified.CREATE OR REPLACE VIEW
is a Greenplum Database language extension. So is the concept of a temporary view.
Parent topic: SQL Command Reference