Select First Row in Each GROUP BY Group in Teradata

event 2020-08-26 visibility 8,169 comment 0 insights
more_vert
insights Stats
Raymond Raymond Teradata

Tutorials and information about Teradata.

As other databases, Teradata provides many aggregation functions that can be used to retrieve SUM, COUNT, MAX, MIN and AVG values. These functions returns a single value per group. To retrieve the whole first row from each 'GROUP BY' group, windowing functions can be used. 

Create sample table 

The following code snippet creates a sample table which will be used to query against. 

create set table TestDb.test_table
(
id int not null,
category varchar(10),
amount int
)
primary index (id);

insert into TestDb.test_table values(1,'A',10);
insert into TestDb.test_table values(2,'A',11);
insert into TestDb.test_table values(3,'A',12);
insert into TestDb.test_table values(4,'B',100);
insert into TestDb.test_table values(5,'B',101);
insert into TestDb.test_table values(6,'B',102);
insert into TestDb.test_table values(4,'C',1000);
insert into TestDb.test_table values(5,'C',1001);
insert into TestDb.test_table values(6,'C',1002);

The content of the table looks like the following:

id category amount
1 A 10
2 A 11
3 A 12
4 B 100
4 C 1,000
5 B 101
5 C 1,001
6 B 102
6 C 1,002

Use FIRST_VALUE function

FISRT_VALUE returns the first value of an ordered set of values. 

Query:

select id, category, amount, 
first_value(amount) over (partition by category order by id) as first_amount
from TestDb.test_table;

Result:

20200826112352-image.png

Window aggregation function

Windows aggregation function MIN can be used to retrieve the minimum value of a window group. 

Query:

select id, category, amount, 
first_value(amount) over (partition by category order by id) as first_amount,
min(amount) over (partition by category) as min_amount
from TestDb.test_table;

Result:

20200826113057-image.png

Retrieve first row in each group

ROW_NUMBER function returns sequential numbers for each row in the window partition and then QUALIFY can be used to eliminate records. 

Query:

select id, category, amount
from TestDb.test_table
qualify row_number() over (partition by category order by id) = 1
;

Result:

20200826113239-image.png

The sample SQL statement returns returns the first row for each category value. 

More from Kontext
comment Comments
No comments yet.

Please log in or register to comment.

account_circle Log in person_add Register

Log in with external accounts