sql - select rownum from salary where rownum=3;

Question

How to retrieve third row from any table using "rownum" key word ( i am using oracle-10g)

Answer 1

Oracle assigns values to ROWNUM sequentially as rows are produced by the query - thus, the first row fetched gets ROWNUM=1, the second row fetched gets ROWNUM=2, the third row fetched gets ROWNUM=3, etc. Notice - for a row to be assigned ROWNUM=3 two preceding rows MUST be fetched. And this is why your query returns no rows. You're asking the database for the third row fetched - but rows 1 and 2 have never been fetched.

To demonstrate, try running the following queries:

SELECT S.* FROM SALARY S;          -- Should return all rows
SELECT ROWNUM, S.* FROM SALARY S;  -- Should return all rows with ROWNUM prepended
SELECT ROWNUM, S.* FROM SALARY WHERE ROWNUM=3;  -- Should return no rows

To work around your problem, try the following:

SELECT ROW_NUMBER FROM
  (SELECT ROWNUM AS ROW_NUMBER, S.* FROM SALARY S)
  WHERE ROW_NUMBER = 3;

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