In the right pane, in the SQL tab for the debugger_tutorial (GROUPO), locate the following statement:

OPEN cursor_this_customer;

Add a breakpoint by clicking the vertical gray area to the left of the statement. The breakpoint appears as a red circle.

In the left pane, right-click debugger_tutorial (GROUPO) and click Execute from Interactive SQL.

In the right pane of Sybase Central, a yellow arrow appears on top of the breakpoint.

In the Debugger Details window, click the Local tab to display a list of local variables in the procedure, along with their current values and data types. The Top_Company, Top_Value, This_Value, and This_Company variables are all uninitialized and are therefore NULL.

Press F11 to scroll through the procedure. The values of the variables change when you reach the following line:

IF SQLSTATE = error_not_found THEN

Press F11 twice more to determine which branch the execution takes. The yellow arrow moves back to the following text:

customer_loop: loop

The IF test did not return true. The test failed because a comparison of any value to NULL returns NULL. A value of NULL fails the test and the code inside the IF...END IF statement is not executed.

At this point, you may realize that the problem is that Top_Value is not initialized.

Test the hypothesis that the problem is the lack of initialization for Top_Value without changing the procedure code: