UCTFIELD"
>amcanunique</TT
> true.
   (At present, only b-tree supports it.)
  </P
><P
>   Because of MVCC, it is always necessary to allow duplicate entries to
   exist physically in an index: the entries might refer to successive
   versions of a single logical row.  The behavior we actually want to
   enforce is that no MVCC snapshot could include two rows with equal
   index keys.  This breaks down into the following cases that must be
   checked when inserting a new row into a unique index:

    <P
></