A procedural language must be “installed” into each
database where it is to be used. But procedural languages installed in
the database template1
are automatically available in all
subsequently created databases, since their entries in
template1
will be copied by CREATE DATABASE
.
So the database administrator can
decide which languages are available in which databases and can make
some languages available by default if desired.
For the languages supplied with the standard distribution, it is
only necessary to execute CREATE EXTENSION
language_name
to install the language into the
current database.
The manual procedure described below is only recommended for
installing languages that have not been packaged as extensions.
Manual Procedural Language Installation
A procedural language is installed in a database in five steps,
which must be carried out by a database superuser. In most cases
the required SQL commands should be packaged as the installation script
of an “extension”, so that CREATE EXTENSION
can be
used to execute them.
The shared object for the language handler must be compiled and installed into an appropriate library directory. This works in the same way as building and installing modules with regular user-defined C functions does; see Section 36.10.5. Often, the language handler will depend on an external library that provides the actual programming language engine; if so, that must be installed as well.
The handler must be declared with the command
CREATE FUNCTIONhandler_function_name
() RETURNS language_handler AS 'path-to-shared-object
' LANGUAGE C;
The special return type of language_handler
tells
the database system that this function does not return one of
the defined SQL data types and is not directly usable
in SQL statements.
Optionally, the language handler can provide an “inline” handler function that executes anonymous code blocks (DO commands) written in this language. If an inline handler function is provided by the language, declare it with a command like
CREATE FUNCTIONinline_function_name
(internal) RETURNS void AS 'path-to-shared-object
' LANGUAGE C;
Optionally, the language handler can provide a “validator”
function that checks a function definition for correctness without
actually executing it. The validator function is called by
CREATE FUNCTION
if it exists. If a validator function
is provided by the language, declare it with a command like
CREATE FUNCTIONvalidator_function_name
(oid) RETURNS void AS 'path-to-shared-object
' LANGUAGE C STRICT;
Finally, the PL must be declared with the command
CREATE [TRUSTED] LANGUAGElanguage_name
HANDLERhandler_function_name
[INLINEinline_function_name
] [VALIDATORvalidator_function_name
] ;
The optional key word TRUSTED
specifies that
the language does not grant access to data that the user would
not otherwise have. Trusted languages are designed for ordinary
database users (those without superuser privilege) and allows them
to safely create functions and
procedures. Since PL functions are executed inside the database
server, the TRUSTED
flag should only be given
for languages that do not allow access to database server
internals or the file system. The languages
PL/pgSQL,
PL/oraSQL
are considered trusted.
In a default LightDB installation, the handlers for the PL/pgSQL and PL/oraSQL languages are built and installed into the “library” directory; furthermore, the PL/pgSQL and PL/oraSQL languages are installed in all databases.