Syntax:

    IMMEDIATE | ON

    This option causes constraint evaluation to be executed
    immediately, when the statement completes. ON is synonymous with
    IMMEDIATE.

    When you issue a SET ALL CONSTRAINTS IMMEDIATE statement, SQL:

    o  Evaluates all previously deferred constraints (those that
       would otherwise be evaluated at a COMMIT statement)

    o  Sets a mode in which SQL evaluates any constraints selected
       for deferred evaluation by the execution of an SQL statement
       at the end of that SQL statement (instead of waiting for a
       COMMIT statement)

    Once the transaction completes, the constraint mode is set back
    to the default constraint mode for subsequent statements.