Highest revision within highest version

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Nice question. Here's one approach:

select P.slno
     , P.partno
     , P.ver
     , P.revision
  from (
       select partno
            , max(ver) as maxver
         from parts
       group
           by partno
       ) as V
inner
  join (
       select partno
            , ver
            , max(revision) as maxrevision
         from parts
       group
           by partno
            , ver
       ) as R
    on R.partno = V.partno
   and R.ver    = V.maxver
inner
  join parts as P
    on P.partno   = R.partno
   and P.ver      = R.ver
   and P.revision = R.maxrevision

Note that this will fail if any of your revision or subrevision numbers goes beyond a single digit. Remember that string columns sort from left to right, not numerically, so here's how they would sort if there were 12 revisions:

1.1
1.10
1.11
1.12
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9

Of course, the query would still be correct! However, you wouldn't get what you thought was the highest (1.12), you'd get what actually was the highest (1.9).