><P
>     A trigger definition can also specify a <TT
CLASS="LITERAL"
>WHEN</TT
>
     condition so that, for example, a <TT
CLASS="LITERAL"
>ddl_command_start</TT
>
     trigger can be fired only for particular commands which the user wishes
     to intercept. A common use of such triggers is to restrict the range of
     DDL operations which users may perform.
   </P
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