Re: offset and limit in update and subselect

"Timothy H. Keitt" <Timothy.Keitt@SUNYSB.Edu> writes:
> Basically, I need to update rows by offset from the beginning of the 
> table.

I think you'd better rethink your data design.  Tuple order in a table
is not a defined concept according to SQL.  Even if we allowed queries
such as you've described, the results would not be well-defined, but
would change at the slightest provocation.  The implementation feels
itself entitled to rearrange tuple order whenever the whim strikes it.

As the documentation tries hard to make plain, LIMIT/OFFSET are only
guaranteed to produce reproducible results if there's also an ORDER BY
that constrains the tuples into a unique ordering.
        regards, tom lane