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-.pgaw:Help.f.t insert end "CREATE LANGUAGE" {bold} ". Using CREATE LANGUAGE, a Postgres user can register a new language with Postgres. Subsequently, functions and trigger procedures can be defined in this new language. The user must \
-have the Postgres superuser privilege to register a new language.
-
-Writing PL handlers
-
- The call handler for a procedural language must be written in a compiler language such as 'C' and registered with Postgres as a function taking no arguments and returning the opaque type, a \
-placeholder for unspecified or undefined types.. This prevents the call handler from being called directly as a function from queries.
-However, arguments must be supplied on the actual call when a PL function or trigger procedure in the language offered by the handler is to be executed. \
- When called from the trigger manager, the only argument is the object ID from the procedure's pg_proc entry. All other information from the trigger manager is found in the global \
- CurrentTriggerData pointer.
- When called from the function manager, the arguments are the object ID of the procedure's pg_proc entry, the number of arguments given to the PL function, the arguments in a \
- FmgrValues structure and a pointer to a boolean where the function tells the caller if the return value is the SQL NULL value.
-
- It's up to the call handler to fetch the pg_proc entry and to analyze the argument and return types of the called procedure. The AS clause from the CREATE FUNCTION of the procedure will \
-be found in the prosrc attribute of the pg_proc table entry. This may be the source text in the procedural language itself (like for PL/Tcl), a pathname to a file or anything else that tells the call \
-handler what to do in detail.
-
-" {} "Synopsis" {bold} "
-
-CREATE \[ TRUSTED \] PROCEDURAL LANGUAGE 'langname'
- HANDLER call_handler
- LANCOMPILER 'comment'
-
-" {code} "Inputs" {bold} "
-
-" {} "TRUSTED" {italic} "
- TRUSTED specifies that the call handler for the language is safe; that is, it offers an unprivileged user no functionality to bypass access restrictions. If this keyword is omitted when
- registering the language, only users with the Postgres superuser privilege can use this language to create new functions (like the 'C' language).
-
-" {} "langname" {italic} "
- The name of the new procedural language. The language name is case insensitive. A procedural language cannot override one of the built-in languages of Postgres.
-
-" {} "HANDLER call_handler" {italic} "
- call_handler is the name of a previously registered function that will be called to execute the PL procedures.
-
-" {} "comment" {italic} "
- The LANCOMPILER argument is the string that will be inserted in the LANCOMPILER attribute of the new pg_language entry. At present, Postgres does not use this attribute in any way.
-
-" {} "Outputs" {bold} "
-
-" {} "CREATE" {italic} "
- This message is returned if the language is successfully created.
-
-" {} "ERROR: PL handler function funcname\(\) doesn't exist" {italic} "
- This error is returned if the function funcname() is not found.
-
-" {} "Usage" {bold} "
-
-This is a template for a PL handler written in 'C':
-" {} "
- #include \"executor/spi.h\"
- #include \"commands/trigger.h\"
- #include \"utils/elog.h\"
- #include \"fmgr.h\" /* for FmgrValues struct */
- #include \"access/heapam.h\"
- #include \"utils/syscache.h\"
- #include \"catalog/pg_proc.h\"
- #include \"catalog/pg_type.h\"
-
- Datum
- plsample_call_handler\(
- Oid prooid,
- int pronargs,
- FmgrValues *proargs,
- bool *isNull\)
- \{
- Datum retval;
- TriggerData *trigdata;
-
- if \(CurrentTriggerData == NULL\) \{
- /*
- * Called as a function
- */
-
- retval = ...
- \} else \{
- /*
- * Called as a trigger procedure
- */
- trigdata = CurrentTriggerData;
- CurrentTriggerData = NULL;
-
- retval = ...
- \}
-
- *isNull = false;
- return retval;
- \}
-" {code} "
-Only a few thousand lines of code have to be added instead of the dots to complete the PL call handler. See CREATE FUNCTION for information on how to compile it into a loadable module .
-
-The following commands then register the sample procedural language:
-" {} "
- CREATE FUNCTION plsample_call_handler () RETURNS opaque
- AS '/usr/local/pgsql/lib/plsample.so'
- LANGUAGE 'C';
-
- CREATE PROCEDURAL LANGUAGE 'plsample'
- HANDLER plsample_call_handler
- LANCOMPILER 'PL/Sample';
-
-" {code} "Notes" {bold} "
-
-Use " {} "CREATE FUNCTION" {bold} " to create a function.
-
-Use DROP LANGUAGE to drop procedural languages.
-
-Refer to the table pg_language for further information:
-
-Table = pg_language
-" {} "
-+-----------------+----------+-------+
-| Field | Type | Length|
-+-----------------+----------+-------+
-| lanname | name | 32 |
-| lancompiler | text | var |
-+-----------------+----------+-------+
-
-lanname |lancompiler
---------+--------------
-internal|n/a
-lisp |/usr/ucb/liszt
-C |/bin/cc
-sql |postgres
-" {code} "
-
-" {} "Restrictions" {bold} "
-
-Since the call handler for a procedural language must be registered with Postgres in the 'C' language, it inherits all the capabilities and restrictions of 'C' functions.
-"