Error behavior
From InterBase
When a procedure encounters an error—either a SQLCODE error, GDSCODE error, or user-defined exception—all statements since the last SUSPEND are undone.
Since select procedures can have multiple SUSPENDs, possibly inside a loop statement, only the actions since the last SUSPEND are undone. Since executable procedures should not use SUSPEND, when an error occurs the entire executable procedure is undone (if EXIT is used, as recommended).