The SQLCA and message vector are two separate host structures
    that SQL declares when it precompiles an INCLUDE SQLCA statement.

    Both the SQLCA and the message vector provide ways of handling
    errors:

    o  The SQLCA is a collection of parameters that SQL uses to
       provide information about the execution of SQL statements
       to application programs. The SQLCODE parameter in the SQLCA
       shows if a statement was successful and, for some errors, the
       particular error when a statement is not successful.

       To illustrate how the SQLCA works in applications, interactive
       SQL displays its contents when you issue the SHOW SQLCA
       statement.

    o  The message vector is also a collection of parameters that
       SQL updates after it executes a statement. It lets programs
       check if a statement was successful, but provides more detail
       than the SQLCA about the type of error if a statement is not
       successful. The message vector, for example, provides a way to
       access any follow-on messages in addition to those containing
       the facility code RDB or SQL.

       You can use the following steps to examine the message
       vector:

       -  Assign any value to the logical name SQL$KEEP_PREP_FILES.

       -  Precompile any program that contains the line "EXEC SQL
          INCLUDE SQLCA". (You can use the programs in the sample
          directory.)

       -  Examine the generated host language program.

    SQL updates the contents of the SQLCA and the message vector
    after completion of every executable SQL statement (nonexecutable
    statements are the DECLARE, WHENEVER, and INCLUDE statements).

    You do not have to use the INCLUDE SQLCA statement in programs.
    However, if you do not, you must explicitly declare the SQLCODE
    parameter to receive values from SQL. SQLCODE is explicitly
    declared as an unscaled, signed longword integer.

    SQLCODE is a deprecated feature of the ANSI/ISO SQL standard
    and is replaced by SQLSTATE. To comply with the ANSI/ISO
    SQL standard, you should explicitly declare either SQLCODE
    or, preferably, SQLSTATE instead of using the INCLUDE SQLCA
    statement. SQLCA (and the INCLUDE SQLCA statement) is not part
    of the ANSI/ISO SQL standard. If you declare SQLCODE or SQLSTATE
    but use the INCLUDE SQLCA statement, SQL uses the SQLCA.

    Programs that do not use the INCLUDE SQLCA statement will
    not have the message vector declared by the precompiler. Such
    programs must explicitly declare the message vector if they:

    o  Use the RDB$LU_STATUS field of the message vector in their
       error checking

    o  Use system calls such as SYS$PUTMSG

    The message vector is not part of the ANSI/ISO SQL standard.

    When the SQLCA structure is explicitly declared by a program,
    SQL does not update the SQLERRD fields. If you want the SQLERRD
    fields updated, include the SQLCA definitions in the program
    using the EXEC SQL INCLUDE SQLCA statement.

    See the Oracle Rdb SQL Reference Manual for more information.