ASA SQL User's Guide
  Using Procedures, Triggers, and Batches
    Errors and warnings in procedures and triggers

Nested compound statements and exception handlers

The code following a statement that causes an error executes only if an ON EXCEPTION RESUME clause appears in a procedure definition.

You can use nested compound statements to give you more control over which statements execute following an error and which do not.

Drop the procedures 

Remember to drop both the InnerProc and OuterProc procedures by entering the following commands in the SQL Statements pane before continuing with the tutorial:

DROP PROCEDURE OuterProc;
DROP PROCEDURE InnerProc

The following demonstration procedure illustrates how nested compound statements can be used to control flow. The procedure is based on that used as an example in Default error handling in procedures and triggers.

CREATE PROCEDURE InnerProc()
BEGIN
   BEGIN
      DECLARE column_not_found
         EXCEPTION FOR SQLSTATE VALUE '52003';
         MESSAGE 'Hello from InnerProc' TO CLIENT;
         SIGNAL column_not_found;
            MESSAGE 'Line following SIGNAL' TO CLIENT
            EXCEPTION
         WHEN column_not_found THEN
            MESSAGE 'Column not found handling' TO
            CLIENT;
         WHEN OTHERS THEN
            RESIGNAL;
   END;
      MESSAGE 'Outer compound statement' TO CLIENT;
END

The following statement executes the InnerProc procedure:

CALL InnerProc();

The Interactive SQL Messages pane then displays the following:

Hello from InnerProc Column not found handling Outer compound statement

When the SIGNAL statement that causes the error is encountered, control passes to the exception handler for the compound statement, and the Column not found handling message prints. Control then passes back to the outer compound statement and the Outer compound statement message prints.

If an error other than column not found is encountered in the inner compound statement, the exception handler executes the RESIGNAL statement. The RESIGNAL statement passes control directly back to the calling environment, and the remainder of the outer compound statement is not executed.