ASA SQL User's Guide
  Transact-SQL Compatibility
    Error handling in Transact-SQL procedures

Transact-SQL-like error handling in the Watcom-SQL dialect

You can make a Watcom-SQL dialect procedure handle errors in a Transact-SQL-like manner by supplying the ON EXCEPTION RESUME clause to the CREATE PROCEDURE statement:

CREATE PROCEDURE sample_proc()
ON EXCEPTION RESUME
BEGIN
   ...
END

The presence of an ON EXCEPTION RESUME clause prevents explicit exception handling code from being executed, so avoid using these two clauses together.