Use the RAISE statement to report messages and raise errors.
RAISE level 'format' [, variable [...]];
Possible levels are DEBUG (write the message to
the server log), LOG (write the message to the
server log with a higher priority), INFO,
NOTICE and WARNING (write
the message to the server log and send it to the client, with
respectively higher priorities), and EXCEPTION
(raise an error and abort the current transaction). Whether error
messages of a particular priority are reported to the client,
written to the server log, or both is controlled by the
CLIENT_MIN_MESSAGES configuration variables. See
the PostgreSQL Administrator's Guide for more
Inside the format string, % is replaced by the
next optional argument's external representation. Write
%% to emit a literal %. Note
that the optional arguments must presently be simple variables,
not expressions, and the format must be a simple string literal.
RAISE NOTICE ''Calling cs_create_job(%)'',v_job_id;
In this example, the value of v_job_id will replace the
% in the string.
RAISE EXCEPTION ''Inexistent ID --> %'',user_id;
This will abort the transaction with the given error message.
PostgreSQL does not have a very smart
exception handling model. Whenever the parser, planner/optimizer
or executor decide that a statement cannot be processed any longer,
the whole transaction gets aborted and the system jumps back
into the main loop to get the next query from the client application.
It is possible to hook into the error mechanism to notice that this
happens. But currently it is impossible to tell what really
caused the abort (input/output conversion error, floating-point
error, parse error). And it is possible that the database backend
is in an inconsistent state at this point so returning to the upper
executor or issuing more commands might corrupt the whole database.
Thus, the only thing PL/pgSQL
currently does when it encounters an abort during execution of a
function or trigger procedure is to write some additional
NOTICE level log messages telling in which
function and where (line number and type of statement) this
happened. The error always stops execution of the function.