How Rownum Works in Pagination Query

How ROWNUM works in pagination query?

You have 4 questions, and all revolve around the usage and functionality of ROWNUM. I will answer each question one-by-one.

Why (this was my first attempt until I search on SO) Select * From Person Where rownum > 100 and rownum < 110; returns 0 rows ?

Nice explanation by Thomas Kyte regarding ROWNUM and pagination here.

A ROWNUM value is assigned to a row after it passes the predicate phase of the query but before the query does any sorting or aggregation. Also, a ROWNUM value is incremented only after it is assigned, which is why the following query will never return a row:

select * 
  from t 
 where ROWNUM > 1;

Because ROWNUM > 1 is not true for the first row, ROWNUM does not advance to 2. Hence, no ROWNUM value ever gets to be greater than 1.

Why there is no simple way to do something like Select ... FROM ... WHERE rownum BETWEEN lowerBound AND upperBound ?

Yes, there is. From Oracle 12c onwards, you could use the new Top-n Row limiting feature. See my answer here.

For example, the below query would return the employees between 4th highest till 7th highest salaries in ascending order:

SQL> SELECT empno, sal
  2  FROM   emp
  3  ORDER BY sal
  4  OFFSET 4 ROWS FETCH NEXT 4 ROWS ONLY;

     EMPNO        SAL
---------- ----------
      7654       1250
      7934       1300
      7844       1500
      7499       1600

SQL>

How to get rid of the r column in the resulting values?

Instead of select *, list the required column names in the outer query. For frequently using the query, creating a view is a simple one time activity.

Alternatively, in SQL*Plus you could use the NOPRINT command. It will not display the column name you don't want to display. However, it would only work in SQL*Plus.

For example,

COLUMN column_name NOPRINT

For example,

SQL> desc dept
 Name                                      Null?    Type
 ----------------------------------------- -------- ------------
 DEPTNO                                             NUMBER(2)
 DNAME                                              VARCHAR2(14)
 LOC                                                VARCHAR2(13)

SQL> COLUMN dname NOPRINT
SQL> COLUMN LOC NOPRINT
SQL> SELECT * FROM dept;

    DEPTNO
----------
        10
        20
        30
        40

SQL>

Does it ensure correct pagination?

Yes, if you write the pagination query correctly.

For example,

SELECT val
FROM   (SELECT val, rownum AS rnum
        FROM   (SELECT val
                FROM   t
                ORDER BY val)
        WHERE rownum <= 8)
WHERE  rnum >= 5;

       VAL
----------
         3
         3
         4
         4

4 rows selected.

SQL>

Or, use the new row limiting feature on 12c as I have shown above.

Few good examples here.

Oracle ROWNUM pagination numbering problem

Why what happened?

• source is select * from user (apparently, false table name; that's reserved for function that returns username of a currently logged user) so it selects all rows from the table
• rownum rnum then reflects number of all rows returned from that table, one-by-one, from 1 to total number of rows in that table
• where rownum <= 10 restricts number of rows returned by the source subquery to 10 (the 1st example) / 200 (the 2nd example). It means that
  
  • the 1st query works with at most 10 rows
  • the 2nd query works with at most 200 rows
• the final filter (where rnum >= 1) returns what's previously being said - at most 10 (or 200) rows

So ... what's the problem? What did you expect to get?

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As of your comment: it seems that order by clause is missing:

select *
from
    (select A.*, ROWNUM RNUM
         from 
        (select * from USER order by name) A
        where ROWNUM <= 10
        order by a.name                 --> this
    ) B
    where RNUM >= 1

Query to insert row number to paginate results

Wrap your query up in a derived table (i.e. the subquery):

select * from
(
  Select ROW_NUMBER() OVER (ORDER BY reputation) as row, *
  From users
  Where reputation > 1000000
) dt
where   row >= ##StartRow:INT?1##
  AND   row    <= ##EndRow:INT?50000##
ORDER BY    row

Note that row is a reserved word according to the ANSI/ISO SQL standard, so you may need to delimit that column name as "row". (Or change it to something else.)

How can I paginate this BigQuery query using the rownumber?

For this example, use a subquery:

SELECT t.*
FROM (SELECT test.id, test.city, ROW_NUMBER() OVER () rownumber
      FROM prod.test LEFT OUTER JOIN
           prod.locations location
           ON test.city = location.id
      WHERE active = true
     ) t 
WHERE rownumber BETWEEN 10000 AND 30000 ;

However, you should probably be using LIMIT and OFFSET.

how to use rownumber to write a paging query in SQL

select * from (
    select ROW_NUMBER() over (order by SalesOrderDate desc) as rn, *
    from sales.salesorderheader
) as x
where rn between @start and @start + @page_size

That ought to do the trick.

Oracle sql rownum between how to shrink the query

How can i shrink it to use one select like that?

Since you are on Oracle 11g you cannot. You must use subquery inline to achieve your desired output.

Select eto.*, eto.rownum rn from employee_trip_orders eto
where rn between 25 and 50 ;

That query will never return a row. ROWNUM value is incremented only after it is assigned. Please see How ROWNUM works in pagination query.

From Oracle 12c onwards, you could use the new Top-n Row limiting feature.

Oracle pagination ROWNUM column=value challenge

I think I have fond a potential solution. However, it's not a query.

declare
cursor c is
SELECT * FROM Measurement WHERE Value >= 1234567890 ORDER BY Value ASC;
l_rec c%rowtype;
begin
    open c;
    for i in 1 .. 2000
    loop
        fetch c into l_rec;
        exit when c%notfound;
    end loop;
    close c;
end;
/

Is order by mandatory for pagination in oracle?

1) Is order by mandatory with OFFSET n ROWS FETCH NEXT m ROWS ONLY?

Syntactically not, semantically it is!

Reason: if you don't add an ORDER BY clause, the database may return the orders in any order. Now if you execute the query first for the first page, you'll get them in any order. The next time you execute the query to fetch the next page may return the orders in any other row.

Therefore you need on ORDER BY clause that establishes a definite order of rows (so that no row is a peer with another row). In practice, you should always include something unique/primary key in the ORDER BY clause to be on the safe side. (you can still use non-unique in the ORDER BY clause — even as leading columns).

e.g.

ORDER BY time_stamp DESC, id DESC

This is a logical requirement for all types of pagination that execute separate queries for each page.

2) Is order by mandatory with RowNum?

Yes, see above.

3) How to create pagination in above sql query using RowNum?

Neither OFFSET nor ROWNUM alone are good enough to implement stable pagination.

Think about this: What if a new row is inserted after you have fetched the first page and before you fetch the second page?

There is another way to implement stable pagination called key-set pagination.

The main idea is not to skip "seen rows" by telling the database how many rows to skip and hoping no rows were added in the meanwhile, but to use a unique identification of which rows have already been seen and which not.

SELECT ...
  FROM ...
 WHERE ...
   AND id < ?last_seen_id
 ORDER BY id DESC
 FETCH FIRST 10 ROWS ONLY

Remember that you need an ORDER BY that establishes a definitie order anyway. You can use these columns to pinpoint the place until where you have received the data before.

Read more about this method at my website:

http://use-the-index-luke.com/no-offset

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