Depending on the implementation language it might also be allowed to specify “pseudo-types” such as cstring. Pseudo-types indicate that the actual argument type is either incompletely specified, or outside the set of ordinary SQL data types.

The type of a column is referenced by writing table_name.column_name%TYPE. Using this feature can sometimes help make a procedure independent of changes to the definition of a table.

The key word EXTERNAL is allowed for SQL conformance, but it is optional since, unlike in SQL, this feature applies to all procedures not only external ones.

A SECURITY DEFINER procedure cannot execute transaction control statements (for example, COMMIT and ROLLBACK, depending on the language).

If a SET clause is attached to a procedure, then the effects of a SET LOCAL command executed inside the procedure for the same variable are restricted to the procedure: the configuration parameter's prior value is still restored at procedure exit. However, an ordinary SET command (without LOCAL) overrides the SET clause, much as it would do for a previous SET LOCAL command: the effects of such a command will persist after procedure exit, unless the current transaction is rolled back.

If a SET clause is attached to a procedure, then that procedure cannot execute transaction control statements (for example, COMMIT and ROLLBACK, depending on the language).

See SET(7) and Chapter 20 for more information about allowed parameter names and values.

It is often helpful to use dollar quoting (see Section 4.1.2.4) to write the procedure definition string, rather than the normal single quote syntax. Without dollar quoting, any single quotes or backslashes in the procedure definition must be escaped by doubling them.

When repeated CREATE PROCEDURE calls refer to the same object file, the file is only loaded once per session. To unload and reload the file (perhaps during development), start a new session.

BEGIN ATOMIC


  statement;


  statement;


  ...


  statement;
END

This is similar to writing the text of the procedure body as a string constant (see definition above), but there are some differences: This form only works for LANGUAGE SQL, the string constant form works for all languages. This form is parsed at procedure definition time, the string constant form is parsed at execution time; therefore this form cannot support polymorphic argument types and other constructs that are not resolvable at procedure definition time. This form tracks dependencies between the procedure and objects used in the procedure body, so DROP ... CASCADE will work correctly, whereas the form using string literals may leave dangling procedures. Finally, this form is more compatible with the SQL standard and other SQL implementations.

CREATE PROCEDURE insert_data(a integer, b integer)
LANGUAGE SQL
AS $$
INSERT INTO tbl VALUES (a);
INSERT INTO tbl VALUES (b);
$$;

CREATE PROCEDURE insert_data(a integer, b integer)
LANGUAGE SQL
BEGIN ATOMIC


  INSERT INTO tbl VALUES (a);


  INSERT INTO tbl VALUES (b);
END;

CALL insert_data(1, 2);