PostgreSQL Errors and Messages

PostgreSQL

Summary: in this tutorial, you will learn how to report messages and raise errors using the raise statement. In addition, you will learn how to use the assert statement to insert debugging checks into PL/pgSQL blocks.


Reporting messages

To raise a message, you use the raise statement as follows:

raise level format;

Let’s examine the raise statement in more detail.

Level

Following the raise statement is the level option that specifies the error severity.

PostgreSQL provides the following levels:

  •  debug
  •  log
  •  notice
  •  info
  •  warning
  •  exception

If you don’t specify the level, by default, the raise statement will use exception level that raises an error and stops the current transaction. We will discuss the raise exception later in the next section.

Format

The format is a string that specifies the message. The format uses percentage ( %) placeholders that will be substituted by the arguments.

The number of placeholders must be the same as the number of arguments, otherwise, PostgreSQL will issue an error:

[Err] ERROR:  too many parameters specified for raise

The following example illustrates the raise statement that reports different messages at the current time.

do $$ 
begin 
  raise info 'information message %', now() ;
  raise log 'log message %', now();
  raise debug 'debug message %', now();
  raise warning 'warning message %', now();
  raise notice 'notice message %', now();
end $$;

Output:

info:  information message 2015-09-10 21:17:39.398+07
warning:  warning message 2015-09-10 21:17:39.398+07
notice:  notice message 2015-09-10 21:17:39.398+07

Notice that not all messages are reported back to the client. PostgreSQL only reports the infowarning, and notice level messages back to the client. This is controlled by client_min_messages and log_min_messages configuration parameters.

Raising errors

To raise an error, you use the exception level after the raise statement. Note that raise statement uses the exception level by default.

Besides raising an error, you can add more information by using the following additional clause:

using option = expression

The option can be:

  • message: set error message
  • hint: provide the hint message so that the root cause of the error is easier to be discovered.
  • detail:  give detailed information about the error.
  • errcode: identify the error code, which can be either by condition name or directly five-character SQLSTATE code. Please refer to the table of error codes and condition names.

The expression is a string-valued expression. The following example raises a duplicate email error message:

do $$ 
declare
  email varchar(255) := 'info@reconshell.com';
begin 
  -- check email for duplicate
  -- ...
  -- report duplicate email
  raise exception 'duplicate email: %', email 
		using hint = 'check the email again';
end $$;
[Err] ERROR:  Duplicate email: info@reconshell.com
HINT:  Check the email again

The following examples illustrate how to raise an SQLSTATE and its corresponding condition:

do $$ 
begin 
	--...
	raise sqlstate '2210b';
end $$;
do $$ 
begin 
	--...
	raise invalid_regular_expression;
end $$;

Now you can use raise statement to either raise a message or report an error.