|PostgreSQL Reference Manual - Volume 2 - Programming Guide|
by The PostgreSQL Global Development Group
Paperback (6"x9"), 408 pages
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8.1 Installing Procedural Languages
A procedural language must be “installed” into each
database where it is to be used. But procedural languages installed in
template1 are automatically available in all
subsequently created databases, since their entries in
template1 will be copied by
So the database administrator can
decide which languages are available in which databases and can make
some languages available by default if he chooses.
For the languages supplied with the standard distribution, it is
only necessary to execute
language_name to install the language into the
current database. Alternatively, the program
createlang may be used to do this from the shell
command line. For example, to install the language
PL/pgSQL into the database
createlang plpgsql template1
The manual procedure described below is only recommended for
installing custom languages that
does not know about.
Manual Procedural Language Installation :
A procedural language is installed in a database in four steps,
which must be carried out by a database superuser. (For languages
- 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 5.9.6 Compiling and Linking Dynamically-Loaded Functions. 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 FUNCTION handler_function_name() RETURNS language_handler AS 'path-to-shared-object' LANGUAGE C;The special return type of
language_handlertells 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 may provide a “validator”
function that checks a function definition for correctness without
actually executing it. The validator function is called by
CREATE FUNCTIONif it exists. If a validator function is provided by the handler, declare it with a command like
CREATE FUNCTION validator_function_name(oid) RETURNS void AS 'path-to-shared-object' LANGUAGE C;
The PL must be declared with the command
CREATE [TRUSTED] [PROCEDURAL] LANGUAGE language-name HANDLER handler_function_name [VALIDATOR validator_function_name] ;The optional key word
TRUSTEDspecifies that ordinary database users that have no superuser privileges should be allowed to use this language to create functions and trigger procedures. Since PL functions are executed inside the database server, the
TRUSTEDflag 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.
CREATE LANGUAGE, the second and third steps can be omitted, because they will be carried out automatically if needed.)
section 8.1 Installing Procedural Languages shows how the manual installation procedure would work with the language PL/pgSQL.
Manual Installation of PL/pgSQL:
The following command tells the database server where to find the shared object for the PL/pgSQL language's call handler function.
CREATE FUNCTION plpgsql_call_handler() RETURNS language_handler AS '$libdir/plpgsql' LANGUAGE C;
PL/pgSQL has a validator function, so we declare that too:
CREATE FUNCTION plpgsql_validator(oid) RETURNS void AS '$libdir/plpgsql' LANGUAGE C;
CREATE TRUSTED PROCEDURAL LANGUAGE plpgsql HANDLER plpgsql_call_handler VALIDATOR plpgsql_validator;
then defines that the previously declared functions
should be invoked for functions and trigger procedures where the
language attribute is
In a default PostgreSQL installation, the handler for the PL/pgSQL language is built and installed into the “library” directory. If Tcl support is configured in, the handlers for PL/Tcl and PL/TclU are also built and installed in the same location. Likewise, the PL/Perl and PL/PerlU handlers are built and installed if Perl support is configured, and the PL/PythonU handler is installed if Python support is configured.
|ISBN 0954612035||PostgreSQL Reference Manual - Volume 2 - Programming Guide||See the print edition|