create sequence of numbers on grouped column in Oracle - sql

Question

Consider below table with column a,b,c.
a b c
3 4 5
3 4 5
6 4 1
1 1 8
1 1 8
1 1 0
1 1 0
I need a select statement to get below output. i.e. increment column 'rn' based on group of column a,b,c.
a b c rn
3 4 5 1
3 4 5 1
6 4 1 2
1 1 8 3
1 1 8 3
1 1 0 4
1 1 0 4

Answer 1

You can use the DENSE_RANK analytic function to get a unique ID for each combination of A, B, and C. Just note that if a new value is inserted into the table, the IDs of each combination of A, B, and C will shift and may not be the same.
Query
WITH
my_table (a, b, c)
AS
(SELECT 3, 4, 5 FROM DUAL
UNION ALL
SELECT 3, 4, 5 FROM DUAL
UNION ALL
SELECT 6, 4, 1 FROM DUAL
UNION ALL
SELECT 1, 1, 8 FROM DUAL
UNION ALL
SELECT 1, 1, 8 FROM DUAL
UNION ALL
SELECT 1, 1, 0 FROM DUAL
UNION ALL
SELECT 1, 1, 0 FROM DUAL)
SELECT t.*, DENSE_RANK () OVER (ORDER BY b desc, c desc, a) as rn
FROM my_table t;
Result
A B C RN
____ ____ ____ _____
3 4 5 1
3 4 5 1
6 4 1 2
1 1 8 3
1 1 8 3
1 1 0 4
1 1 0 4

Answer 2

As a starter: for your answer to make sense at all, you need a column that defines the ordering of the rows. Let me assume that you have such column, called id.
Then, you can use window functions:
select a, b, c,
sum(case when a = lag_a and b = lag_b and c = lag_c then 0 else 1 end) over(order by id) rn
from (
select t.*,
lag(a) over(order by id) lag_a,
lag(b) over(order by id) lag_b,
lag(c) over(order by id) lag_c
from mytable t
) t

Answer 3

Assuming you have some way of ordering your rows, then you can use MATCH_RECOGNIZE:
SELECT a, b, c, rn
FROM table_name
MATCH_RECOGNIZE (
ORDER BY id
MEASURES MATCH_NUMBER() AS rn
ALL ROWS PER MATCH
PATTERN ( FIRST_ROW EQUAL_ROWS* )
DEFINE EQUAL_ROWS AS (
EQUAL_ROWS.a = PREV( EQUAL_ROWS.a )
AND EQUAL_ROWS.b = PREV( EQUAL_ROWS.b )
AND EQUAL_ROWS.c = PREV( EQUAL_ROWS.c )
)
)
So, for your test data:
CREATE TABLE table_name ( id, a, b, c ) AS
SELECT 1, 3, 4, 5 FROM DUAL UNION ALL
SELECT 2, 3, 4, 5 FROM DUAL UNION ALL
SELECT 3, 6, 4, 1 FROM DUAL UNION ALL
SELECT 4, 1, 1, 8 FROM DUAL UNION ALL
SELECT 5, 1, 1, 8 FROM DUAL UNION ALL
SELECT 6, 1, 1, 0 FROM DUAL UNION ALL
SELECT 7, 1, 1, 0 FROM DUAL;
Outputs:
A | B | C | RN
-: | -: | -: | -:
3 | 4 | 5 | 1
3 | 4 | 5 | 1
6 | 4 | 1 | 2
1 | 1 | 8 | 3
1 | 1 | 8 | 3
1 | 1 | 0 | 4
1 | 1 | 0 | 4
db<>fiddle here

Answer 4

It can also be done without any ordering, by getting the distinct groups and numbering each group. Borrowing the first part from EJ Egjed:
WITH my_table (a, b, c) AS
(SELECT 3, 4, 5 FROM DUAL
UNION ALL
SELECT 3, 4, 5 FROM DUAL
UNION ALL
SELECT 6, 4, 1 FROM DUAL
UNION ALL
SELECT 1, 1, 8 FROM DUAL
UNION ALL
SELECT 1, 1, 8 FROM DUAL
UNION ALL
SELECT 1, 1, 0 FROM DUAL
UNION ALL
SELECT 1, 1, 0 FROM DUAL)
, groups as (select distinct a, b, c
from my_table)
, groupnums as (select rownum as num, a, b, c
from groups)
select a, b, c, num
from my_table join groupnums using(a,b,c);