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.

1. 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 39.10.5. 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.

2. The handler must be declared with the command

   CREATE FUNCTION handler_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.

3. 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 FUNCTION inline_function_name(internal)
       RETURNS void
       AS 'path-to-shared-object'
       LANGUAGE C;
   

4. 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 FUNCTION validator_function_name(oid)
       RETURNS void
       AS 'path-to-shared-object'
       LANGUAGE C STRICT;
   

5. Finally, the PL must be declared with the command

   CREATE [TRUSTED] LANGUAGE language_name
       HANDLER handler_function_name
       [INLINE inline_function_name]
       [VALIDATOR validator_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/Tcl, and PL/Perl are considered trusted; the languages PL/TclU, PL/PerlU, and PL/PythonU are designed to provide unlimited functionality and should not be marked trusted.