Use the RAISE statement to report messages and raise errors.
Possible levels are DEBUG, LOG, INFO, NOTICE, WARNING, and EXCEPTION. EXCEPTION raises an error (which normally aborts the current transaction); the other levels only generate messages of different priority levels. Whether messages of a particular priority are reported to the client, written to the server log, or both is controlled by the log_min_messages and client_min_messages configuration variables. See Chapter 17 for more information.
Inside the format string, % is replaced by the next optional argument's string representation. Write %% to emit a literal %. Arguments can be simple variables or expressions, and the format must be a simple string literal.
In this example, the value of v_job_id will replace the % in the string:
RAISE NOTICE 'Calling cs_create_job(%)', v_job_id;
This example will abort the transaction with the given error message:
RAISE EXCEPTION 'Nonexistent ID --> %', user_id;
RAISE EXCEPTION presently always generates the same SQLSTATE code, P0001, no matter what message it is invoked with. It is possible to trap this exception with EXCEPTION ... WHEN RAISE_EXCEPTION THEN ... but there is no way to tell one RAISE from another.