Sequentially number rows by keyed group in SQL?

Question

Is there a way in SQL to sequentially add a row number by key group?

Assume a table with arbitrary (CODE,NAME) tuples. Example table:

CODE NAME    
---- ----
A    Apple
A    Angel
A    Arizona
B    Bravo
C    Charlie
C    Cat
D    Dog
D    Doppler
D    Data
D    Down

Desired projection using CODE as the grouping attribute:

CODE C_NO NAME    
---- ---- ----
A    0    Apple
A    1    Angel
A    2    Arizona
B    0    Bravo
C    1    Charlie
C    0    Cat
D    0    Dog
D    1    Data
D    2    Down
D    3    Doppler

Thanks,

gbn · Accepted Answer · 2011-03-28T18:38:04.123

39

MySQL doesn't AFAIK. This covers most bases..

SELECT
    CODE,
    ROW_NUMBER() OVER (PARTITION BY CODE ORDER BY NAME) - 1 As C_NO,
    NAME
FROM
    MyTable

edited Mar 28 '11 at 18:38

answered Mar 28 '11 at 18:31

gbn

394,550
75
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647

Was wondering if this could be agnostic, but it is on Oracle. – Jé Queue Mar 28 '11 at 18:35

ypercubeᵀᴹ · Answer 2 · 2011-03-28T19:45:49.903

MySQL (and probably most other databases):

select g.CODE
     , count(*)-1 as C_NO
     , g.NAME
from MyTable as g
  left join MyTable as o
    on g.CODE = o.CODE
      and g.NAME >= o.NAME
group by g.CODE
       , g.NAME;

Specific to MySQL:

DELIMITER $$
CREATE PROCEDURE NumberRowsByGroup()
BEGIN
  SET  @code := 0;
  SET  @num := 0;
  SELECT CODE, C_NO, NAME FROM
    ( select q.CODE
           , q.NAME
           , @num := IF(q.CODE = @code, @num + 1, 0) as C_NO
           , @code := q.CODE as previous
      from yourTable q
      order by CODE
             , NAME
    ) as p
  ;
END$$
DELIMITER ;

Then, we can call:

CALL NumberRowsByGroup();

According to xaprb.com/blog post: how-to-number-rows-in-mysql, the second is faster.

The first solution isn't needed on other RDBMS that have windowing functions — gbn, Apr 03 '11 at 09:29

Sequentially number rows by keyed group in SQL?

2 Answers2

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