CREATE EXTENSION — install an extension
CREATE EXTENSION [ IF NOT EXISTS ]extension_name[ WITH ] [ SCHEMAschema_name] [ VERSIONversion] [ CASCADE ]
CREATE EXTENSION loads a new extension into the current
database. There must not be an extension of the same name already loaded.
Loading an extension essentially amounts to running the extension's script
file. The script will typically create new SQL objects such as
functions, data types, operators and index support methods.
CREATE EXTENSION additionally records the identities
of all the created objects, so that they can be dropped again if
DROP EXTENSION is issued.
The user who runs CREATE EXTENSION becomes the
owner of the extension for purposes of later privilege checks, and
normally also becomes the owner of any objects created by the
extension's script.
Loading an extension ordinarily requires the same privileges that would
be required to create its component objects. For many extensions this
means superuser privileges are needed.
However, if the extension is marked trusted in
its control file, then it can be installed by any user who has
CREATE privilege on the current database.
In this case the extension object itself will be owned by the calling
user, but the contained objects will be owned by the bootstrap superuser
(unless the extension's script explicitly assigns them to the calling
user). This configuration gives the calling user the right to drop the
extension, but not to modify individual objects within it.
IF NOT EXISTSDo not throw an error if an extension with the same name already exists. A notice is issued in this case. Note that there is no guarantee that the existing extension is anything like the one that would have been created from the currently-available script file.
extension_name
The name of the extension to be
installed. LightDB will create the
extension using details from the file
SHAREDIR/extension/extension_name.control.
schema_nameThe name of the schema in which to install the extension's objects, given that the extension allows its contents to be relocated. The named schema must already exist. If not specified, and the extension's control file does not specify a schema either, the current default object creation schema is used.
If the extension specifies a schema parameter in its
control file, then that schema cannot be overridden with
a SCHEMA clause. Normally, an error will be raised if
a SCHEMA clause is given and it conflicts with the
extension's schema parameter. However, if
the CASCADE clause is also given,
then schema_name is
ignored when it conflicts. The
given schema_name will be
used for installation of any needed extensions that do not
specify schema in their control files.
Remember that the extension itself is not considered to be within any schema: extensions have unqualified names that must be unique database-wide. But objects belonging to the extension can be within schemas.
versionThe version of the extension to install. This can be written as either an identifier or a string literal. The default version is whatever is specified in the extension's control file.
CASCADE
Automatically install any extensions that this extension depends on
that are not already installed. Their dependencies are likewise
automatically installed, recursively. The SCHEMA clause,
if given, applies to all extensions that get installed this way.
Other options of the statement are not applied to
automatically-installed extensions; in particular, their default
versions are always selected.
Before you can use CREATE EXTENSION to load an extension
into a database, the extension's supporting files must be installed.
Information about installing the extensions supplied with
LightDB can be found in
Additional Supplied Modules.
The extensions currently available for loading can be identified from the
pg_available_extensions
or
pg_available_extension_versions
system views.
Installing an extension as superuser requires trusting that the
extension's author wrote the extension installation script in a secure
fashion. It is not terribly difficult for a malicious user to create
trojan-horse objects that will compromise later execution of a
carelessly-written extension script, allowing that user to acquire
superuser privileges. However, trojan-horse objects are only hazardous
if they are in the search_path during script
execution, meaning that they are in the extension's installation target
schema or in the schema of some extension it depends on. Therefore, a
good rule of thumb when dealing with extensions whose scripts have not
been carefully vetted is to install them only into schemas for which
CREATE privilege has not been and will not be granted to any untrusted
users. Likewise for any extensions they depend on.
The extensions supplied with LightDB are believed to be secure against installation-time attacks of this sort, except for a few that depend on other extensions. As stated in the documentation for those extensions, they should be installed into secure schemas, or installed into the same schemas as the extensions they depend on, or both.
For information about writing new extensions, see Section 36.17.
Install the hstore extension into the
current database, placing its objects in schema addons:
CREATE EXTENSION hstore SCHEMA addons;
Another way to accomplish the same thing:
SET search_path = addons; CREATE EXTENSION hstore;
CREATE EXTENSION is a LightDB
extension.