Invokes an external or stored procedure from within a compound
    statement. That is, invocation must occur with a BEGIN . . . END
    block.

    The OUT and INOUT arguments cannot be general value expressions.
    They must be variables or parameters. The IN argument can be a
    general value expression.

    When you register a procedure definition with the CREATE
    PROCEDURE statement, you store information in the database
    about an external procedure written in a 3GL language. External
    procedures reside outside the database. The CREATE PROCEDURE
    statement is documented under the CREATE Routine. See the CREATE
    Routine for more information on creating external procedures.

    For optional information on invoking stored procedures, see the
    CALL Simple_Statement.