Saturday, December 27, 2014

Analytical function: ROW_NUMBER () with Qualify in Teradata

This post will help to understand QUALIFY  ROW_NUMBER OVER (PARTITION BY ...) phrase with simple example.

We take an example like below:

INDUST_CODE
INDUSTRY_NAME
ACTIVATE_DATE
1011
GOOGLE
13-12-2009
1013
YOUTUBE
01-09-2008
1011
GOOGLE
15-12-2009
1012
MICROSOFT
14-10-1999
1011
GOOGLE
11-12-2009

The data listed above have more than one row with Industry named ‘Google’.  Business needs the industry name without duplication, they don’t want one industry name more than once. They like to see the data like below:

INDUST_CODE
 INDUSTRY_NAME

1011
GOOGLE

1012
MICROSOFT

1013
YOUTUBE


How do you do that?
You are expert in SQL, so wrote the script like below which works fine:
select INDUST_CODE,INDUSTRY_NAME
from INDUSTRY
QUALIFY
row_number() Over (partition by INDUST_CODE order by ACTIVATE_DATE desc)=1

If you want to know how the code worked? Then please find the explanation step by step:
1) Group by (Partition by)with Industry Code (INDUST_CODE)
2) Order by with ACTIVATE_DATE which means latest date will be used to find the first row
3) Then uses ‘QUALIFY’ to select the row.

Lets explain the syntax :





















Make the translation easy:
qualify row_number() over (Partition and order by brace) = 1
    which means,
    Selecting first row from the result set after applying group by and order by function. 



7 comments:

Kumar P said...

Hi,

Could you please confirm whether this applies for deleting the dupes as well

Kumar P said...

Hi,

Could you please suggest whether this code can be converted to delete the duplicate records

dipu paul said...

HI Kumar, it can be used to delete the rows at the same way. For example:
Delete from
and then the code...

Manish said...

HI Dipu,

Qualify can not be used in delete statement.

Anonymous said...

Hi Dipu,

What is the advantage of using this instead of "select distinct industry_code, industry"?

Krishna said...

Why don't we write a simple select distinct statement to select unique values.

Diponkar Paul said...

Hi Krishna, I hope you already know by now that why we need analytical function in SQL?