I don't know the difference of using index clause and just constraint clause

Hi.. there..
I don't know the difference of 'using index' clause and just primary key constraint...

detail...
1.Create Table testtable(
  test number(4) constraint ...primary key   using index ....
  ...)
=>create a unique index for primary key...(it's explicit)
2.Create Table testtable(
  test number(4) constraint ... primary key    ..)=>create a unique index for primary key...(it's implicit & not use 'using index clause)

pls..let's me know the difference of No.1 and No.2 Received on Thu Aug 16 2001 - 23:21:38 CDT