Displays the default setting for constraint evaluation for any
    transactions starting after the current transaction. If there is
    a current transaction, displays the constraint evaluation mode
    for the current transaction.

    When the constraint mode is IMMEDIATE, SQL evaluates all commit-
    time constraints at the end of each statement and at commit time,
    until the transaction completes or until you set the constraint
    mode to OFF. When the constraint mode is DEFERRED (the default
    setting), constraint evaluation is deferred until commit time.