SQL Query With Row_Number, order by and where clause.

Question

I have the following SQL querry:

select
     ID, COLUMN1, COLUMN2
from
     (select ID, COLUMN1, COLUMN2, row_number() over (order by 2 DESC) NO from A_TABLE)
where
     NO between 0 and 100

What I am trying to do is to select the first 100 records of the query select ID, COLUMN1, COLUMN2 from ATABLE order by 2 DESC

And here are the problems:

1. Apparently, the order by clause is not working. I've noticed that I have to add another "order by 2 DESC" clause, just after "(...) from ATABLE", for my querry to work. Is there something I do wrong? Or is it expectead behaviour?

2. How can I add a where clause? Let's say I need to select only the first 100 records of the table "where COLUMN1 like '%value%'". I've tried adding the where clause after "(...) from ATABLE" but it produced an error...

Help? Tnks.

PS: I'm using Oracle 10g R2.

Answer 1

Why don't you use

Select top 100 ID, Column1, Column2
From A_Table
where Column1 like '%value%'
order by Column2 desc

Answer 2

rownum is a pseudo column that counts rows in the result set after the where clause has been applied.

Is this what you're trying to get?

SELECT *
FROM ( 
    SELECT id, column1, column2
    FROM atable ORDER BY 2 DESC
) 
WHERE ROWNUM < 100;

Because it's a pseudo column that is strictly a counter of rows resulting from the where clause it will not allow you to do pagination (i.e. between 200 & 300).

This is probably what you're looking for:

SELECT *
FROM
 (SELECT a.*, rownum rnum FROM
     (SELECT id, column1, column2 FROM atable ORDER BY 2 DESC) a WHERE rownum <= 300)
WHERE rnum >= 200;

Answer 3

Check out this Oracle FAQ. In particular this part:

  SELECT * 
  FROM (SELECT a.*, rownum RN 
      FROM (SELECT * 
                         FROM t1 ORDER BY key_column) a
         WHERE rownum <=7)
 WHERE rn >=5

Answer 4

To answer your first question: Don't use a column number in your order by clause, but use the column name. I don't fully understand your second question, because adding a WHERE in your most inner SELECT should do the trick:

select ID
,      COLUMN1
,      COLUMN2
from  (select ID
       ,      COLUMN1
       ,      COLUMN2
       ,      row_number() over (order by COLUMN1 DESC) NO
       from   A_TABLE
       where  COLUMNX LIKE '%SOME VALUE%'
      )
where  NO between 0 and 100

P.S. (to willcodejavaforfood) I think using row_number() is better when you want the rows to be ordered. It saves an inner view (big win for readability).