The general form of handler declaration is:

DECLARE <handler_type> HANDLER FOR
        <condition> [, <condition [...]]
        <sql_procedure_statement>;

For compatibility handlers can be declared also as :

WHENEVER <condition> [GOTO <label>|DEFAULT];

When Virtuoso raises a condition that matches the <condition>, the <sql_procedure_statement> gets executed and when (and if) it finishes the execution continues according to the <handler_type>.

<handler_type>

CONTINUE - Specifies that after <sql_procedure_statement> completes, execution continues with the statement after the statement which caused the error.

EXIT - Specifies that after <sql_procedure_statement> completes, execution continues after the end of the compound statement that contains the declaration of the handler.

<condition>

NOT FOUND - Identifies any condition that results in SQL STATE = SQL_NO_DATA_FOUND (+100)

SQLEXCEPTION - Identifies all character SQL STATEs excluding ones starting with '01', '02' and '00'

SQLWARNING - Identifies character SQL STATEs starting with '01'. This is a shortcut for SQLSTATE '01*'

SQLSTATE [VALUE] '<sql_state_mask>' - Identifies character SQL STATEs. The <sql_state_mask> can be a full 5 character value or 0-4 characters followed by an '*'. When a '*' is present then any SQL STATE signal led which starts with the same characters as the <sql_state_mask> before the '*' will cause that handler to execute. For example the exception with SQL state '42S22' will match all the following

SQLSTATE <conditions> :
SQLSTATE '*' SQLSTATE '42*'
SQLSTATE '42S22'
[Note] Note:

Handler's call priority is determined by the number of matching characters in this mask.

<sql_procedure_statement>

This can be any allowed Virtuoso/PL statement as well as an compound statement. This statement is executed in the same procedure context as the procedure body itself, so any labels and variables in the procedure body can be used and RETURN causes the procedure to end. No handler is active while the <sql_procedure_statement> is executed. So any exception raised is passed directly to the procedure caller. The <sql_procedure_statement> can be empty resulting in the <handler_type> action being taken right after setting the __SQL_STATE & __SQL_MESSAGE variables.

When multiple active handlers <condition>s match the exception being raised Virtuoso chooses the closest to the statement raised the exception that has a largest call priority. This means that if an exception is there are two handlers with condition SQLSTATE '4*' and SQLSTATE '42*' and an exception with SQL STATE '42S22' is raised the handler with <condition> '42*' will be called.

WHENEVER <condition> GOTO <label>

is an equivalent of:

DECLARE EXIT HANDLER FOR <condition> GOTO label.
WHENEVER <condition> DEFAULT

is equivalent of:

DECLARE EXIT HANDLER FOR <condition> RESIGNAL;

The following examples demonstrate simple common handlers:

CONTINUE handler: The handler assigns a value of 1 to a local variable at_end when a NOT FOUND condition is raised. The execution then continues with the statement after the signal.

create procedure test1 ()
{
  declare at_end integer;

  at_end := 0;
  declare continue handler for NOT FOUND at_end := 1;

  result_names (at_end);

  result (at_end);
  signal (100);
  result (at_end);
}

When this procedure gets executed it returns the following result set :

0
1

EXIT handler: The handler assigns a value of 2 to a local variable at_end when a NOT_FOUND condition is raised. The execution then continues with the statement after the compound statement containing the signal.

create procedure test2 ()
{
  declare at_end integer;

  result_names (at_end);

  at_end := 0;
  declare exit handler for NOT FOUND at_end := 1;

    {
      result (at_end);
      signal (100);
      result (3);
    }
  result (at_end);
}

When this procedure gets executed it returns the following result set :

0
1
__SQL_STATE and __SQL_MESSAGE variables.

All Virtuoso/PL procedure have two variables implicitly declared :

declare __SQL_STATE any;
declare __SQL_MESSAGE varchar;

Initially they are set to 0.

When an exception is raised these variables are set as follows :

__SQL_STATE gets the SQL STATE (character string or integer 100 for NOT FOUND)
__SQL_MESSAGE gets the SQL MESSAGE (character) or NULL if no message.

Their values are preserved until the next exception overwrites them.

RESIGNAL statement

Syntax :
RESIGNAL [ '<new_sql_state>' ]

RESIGNAL  is a shortcut for    signal (__SQL_STATE, __SQL_MESSAGE)
RESIGNAL '<new_sql_state>' is a shortcut for     signal ('<new_sql_state>', __SQL_MESSAGE);

This statement resignals the current exception to the caller of the procedure.