Question

select top N from a table in oracle

Asked by: kuntilanak

I tried to get the top highest 5 of the M_FFB score attribute from a table/relation, why is it that this returns a NULL when I tried to print the M_FFB while there are higher scores when I tried to run the following SQL statement?

SELECT SName, M_FFB FROM (SELECT * FROM table2004 ORDER BY M_FFB DESC) WHERE ROWNUM < 6;

                                  
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Asked On
2009-11-04 at 14:17:19ID24872740
Topics

SQL Query Syntax

,

Oracle Database

,

Databases Miscellaneous

Participating Experts
1
Points
500
Comments
14

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Answers

 

by: angelIIIPosted on 2009-11-04 at 14:19:43ID: 25744644

 

by: kuntilanakPosted on 2009-11-04 at 14:21:23ID: 25744662

so you mean instead of ROWNUM I should use ROW_NUMBER?

 

by: angelIIIPosted on 2009-11-04 at 14:23:24ID: 25744684

no.

SELECT SName, M_FFB 
 FROM (SELECT t.* 
            , ROW_NUMBER() OVER (ORDER BY M_FFB DESC) rn
        FROM table2004 t 
       )
 WHERE rn  < 6;

                                              
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by: kuntilanakPosted on 2009-11-04 at 14:26:41ID: 25744719

well now it doesn't return NULL, but I can't see the value.. when you order a particular column by some attribute, does the value with a NULL gets ordered on the top row.. that's what I assume...

 

by: angelIIIPosted on 2009-11-04 at 14:30:01ID: 25744759

which value?

to skip NULL

SELECT SName, M_FFB 
 FROM (SELECT t.* 
            , ROW_NUMBER() OVER (ORDER BY CASE WHEN M_FFB IS NULL THEN 1 ELSE 0 END, M_FFB DESC) rn
        FROM table2004 t 
       )
 WHERE rn  < 6;

                                              
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by: kuntilanakPosted on 2009-11-04 at 14:32:32ID: 25744782

how do you skip NULL in this statement, I like this one better as it's shorter... I want those that has M_FFB as NULL to be not included in the resulting query

SELECT SName, M_FFB FROM (SELECT * FROM table2004 ORDER BY M_FFB DESC) WHERE ROWNUM < 6;
                                              
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by: angelIIIPosted on 2009-11-04 at 14:35:07ID: 25744808

SELECT SName, M_FFB FROM (SELECT * FROM table2004 WHERE M_FFB IS NOT NULL ORDER BY M_FFB DESC) WHERE ROWNUM < 6;

 

by: kuntilanakPosted on 2009-11-04 at 15:13:52ID: 25745162

if I did the SQL statement you wrote above for several tables, and wish to have the resulting query of each table sorted in descending order based on the M_FFB value, how can I do this?

 

by: angelIIIPosted on 2009-11-04 at 15:15:30ID: 25745174

a UNION query?
please clarify

 

by: kuntilanakPosted on 2009-11-04 at 15:28:08ID: 25745290

yes my query looks like this now

However, for each year there will be 5 results and I want those 5 results in descending order... for some reason when I union all those.. each year the results isn't descending anymore, instead of ascending

SELECT '2007' AS YEAR,M_FFB ,SName FROM (SELECT * FROM AIMSspring2007 WHERE M_FFB IS NOT NULL ORDER BY M_FFB DESC) WHERE ROWNUM < 6 union SELECT '2006' AS YEAR,M_FFB ,SName FROM (SELECT * FROM AIMSspring2006 WHERE M_FFB IS NOT NULL ORDER BY M_FFB DESC) WHERE ROWNUM < 6 union SELECT '2005' AS YEAR,M_FFB ,SName FROM (SELECT * FROM AIMSspring2005 WHERE M_FFB IS NOT NULL ORDER BY M_FFB DESC) WHERE ROWNUM < 6 union SELECT '2004' AS YEAR,M_FFB ,SName FROM (SELECT * FROM AIMSspring2004 WHERE M_FFB IS NOT NULL ORDER BY M_FFB DESC) WHERE ROWNUM < 6
                                              
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by: angelIIIPosted on 2009-11-04 at 15:31:09ID: 25745314

please try this code.

note: you might consider using partitioned tables...

select *
 FROM ( SELECT '2007' AS YEAR,M_FFB ,SName 
FROM (SELECT * FROM AIMSspring2007 WHERE M_FFB IS NOT NULL ORDER BY M_FFB DESC) 
WHERE ROWNUM < 6 )
union all 
select *
 FROM ( SELECT '2006' AS YEAR,M_FFB ,SName 
FROM (SELECT * FROM AIMSspring2006 WHERE M_FFB IS NOT NULL ORDER BY M_FFB DESC) WHERE ROWNUM < 6 )
union all
select *
 FROM ( SELECT '2005' AS YEAR,M_FFB ,SName FROM (SELECT * FROM AIMSspring2005 WHERE M_FFB IS NOT NULL ORDER BY M_FFB DESC) WHERE ROWNUM < 6 
)
UNION ALL
select *
 FROM ( SELECT '2004' AS YEAR,M_FFB ,SName FROM (SELECT * FROM AIMSspring2004 WHERE M_FFB IS NOT NULL ORDER BY M_FFB DESC) WHERE ROWNUM < 6 )
                                              
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by: kuntilanakPosted on 2009-11-04 at 15:37:23ID: 25745368

what is the different of your code above and mine?

 

by: kuntilanakPosted on 2009-11-04 at 17:05:48ID: 25745886

the union all and union?

 

by: angelIIIPosted on 2009-11-04 at 22:44:35ID: 25747222

yes, union all mainly, as union alone does a implicit distinct... which is unneeded in your query, as the data returned will be distinct anyway.

20120131-EE-VQP-002

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