Why does CONNECT BY LEVEL on a table return extra rows?

Question

Using CONNECT BY LEVEL seems to return too many rows when performed on a table. What is the logic behind what\'s happening?

Assuming the following table:

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Answer 1

You can use technique below to overcome this issue:

select id, level as lvl
   from a
      left outer join (select level l from dual connect by level <= 2) lev on 1 = 1
order by id