SQL Find duplicate with several field (no unique ID) WORK AROUND

Question

I am trying to find duplicated vendors from a database using several fields from vendor table and vendor_address table. The thing is the more inner join I mak

Answer 1

Lets have some interesting data with chained duplicates on different attributes:

CREATE TABLE data ( ID, A, B, C ) AS
  SELECT 1, 1, 1, 1 FROM DUAL UNION ALL -- Related to #2 on column A
  SELECT 2, 1, 2, 2 FROM DUAL UNION ALL -- Related to #1 on column A, #3 on B & C, #5 on C
  SELECT 3, 2, 2, 2 FROM DUAL UNION ALL -- Related to #2 on columns B & C, #5 on C
  SELECT 4, 3, 3, 3 FROM DUAL UNION ALL -- Related to #5 on column A
  SELECT 5, 3, 4, 2 FROM DUAL UNION ALL -- Related to #2 and #3 on column C, #4 on A
  SELECT 6, 5, 5, 5 FROM DUAL;          -- Unrelated

Now, we can get some relationships using analytic functions (without any joins):

SELECT d.*,
       LEAST(
         FIRST_VALUE( id ) OVER ( PARTITION BY a ORDER BY id ),
         FIRST_VALUE( id ) OVER ( PARTITION BY b ORDER BY id ),
         FIRST_VALUE( id ) OVER ( PARTITION BY c ORDER BY id )
       ) AS duplicate_of
FROM   data d;

Which gives:

ID A B C DUPLICATE_OF
-- - - - ------------
 1 1 1 1            1
 2 1 2 2            1
 3 2 2 2            2
 4 3 3 3            4
 5 3 4 2            2
 6 5 5 5            6

But that doesn't pick up that #4 is related to #5 which is related to #2 and then to #1...

This can be found with a hierarchical query:

SELECT id, a, b, c,
       CONNECT_BY_ROOT( id ) AS duplicate_of
FROM   data
CONNECT BY NOCYCLE ( PRIOR a = a OR PRIOR b = b OR PRIOR c = c );

But that will give many, many duplicate rows (since it does not know where to start the hierarchy from so will chose each row in turn as the root) - instead you can use the first query to give the hierarchical query a starting point when the ID and DUPLICATE_OF values are the same:

SELECT id, a, b, c,
       CONNECT_BY_ROOT( id ) AS duplicate_of
FROM   (
  SELECT d.*,
         LEAST(
           FIRST_VALUE( id ) OVER ( PARTITION BY a ORDER BY id ),
           FIRST_VALUE( id ) OVER ( PARTITION BY b ORDER BY id ),
           FIRST_VALUE( id ) OVER ( PARTITION BY c ORDER BY id )
         ) AS duplicate_of
  FROM   data d
)
START WITH id = duplicate_of
CONNECT BY NOCYCLE ( PRIOR a = a OR PRIOR b = b OR PRIOR c = c );

Which gives:

ID A B C DUPLICATE_OF
-- - - - ------------
 1 1 1 1            1
 2 1 2 2            1
 3 2 2 2            1
 4 3 3 3            1
 5 3 4 2            1
 1 1 1 1            4
 2 1 2 2            4
 3 2 2 2            4
 4 3 3 3            4
 5 3 4 2            4
 6 5 5 5            6

There are still some rows are duplicated because of the local minima in the search that occurs a #4 ... which can be removed with a simple GROUP BY:

SELECT id, a, b, c,
       MIN( duplicate_of ) AS duplicate_of
FROM   (
  SELECT id, a, b, c,
         CONNECT_BY_ROOT( id ) AS duplicate_of
  FROM   (
    SELECT d.*,
           LEAST(
             FIRST_VALUE( id ) OVER ( PARTITION BY a ORDER BY id ),
             FIRST_VALUE( id ) OVER ( PARTITION BY b ORDER BY id ),
             FIRST_VALUE( id ) OVER ( PARTITION BY c ORDER BY id )
           ) AS duplicate_of
    FROM   data d
  )
  START WITH id = duplicate_of
  CONNECT BY NOCYCLE ( PRIOR a = a OR PRIOR b = b OR PRIOR c = c )
)
GROUP BY id, a, b, c;

Which gives the output:

ID A B C DUPLICATE_OF
-- - - - ------------
 1 1 1 1            1
 2 1 2 2            1
 3 2 2 2            1
 4 3 3 3            1
 5 3 4 2            1
 6 5 5 5            6