Question

I have a table (T1) and a table with attributes (T2). I’m looking to find records that have the same attributes as a record with provided id.

Here’s the example. Given 1 I want to find 2 (ensuring that attributes match as well).

T1
ID | A | B
----------
1  | k | l
2  | k | l


T2
IDFK | C | D
-------------    
1    | w | x
1    | y | z
2    | w | x
2    | y | z

Here’s the SQL I have so far:

SELECT * FROM T1 
JOIN T1 AS T1COPY ON T1.A = T1COPY.A, T1.B = T1COPY.B 
JOIN T2 ON T1.ID = T2.IDFK 
JOIN T2 AS T2COPY ON T1COPY.ID = T2COPY.IDFK 
   AND T2.C = T2COPY.C 
   AND T2.D = T2COPY.D
WHERE T1.ID = 1

but it’s not working right as it’s matching 2 even if attributes are different.

Answer 1

Here’s the answer for MySQL: http://www.sqlfiddle.com/#!2/ec4fa/2

select h.* 
from 
(
    select x.*
    from t join t x using(a,b)
    where t.id = 1 and x.id <> 1  
) h
join 
(

    select coalesce(x.cpIdFk, x.uIdFk) as idFk  
    from
    (
      select cp.idFk as cpIdFk, u.idFk as uIdFk
      from 
      (
        select t.id as idFk, x.*
        from t cross join (select c, d from u where idFk = 1) as x
        where t.id <> 1      
      ) cp
      left join (select * from u where idFk <> 1) u using(idfk,c,d)

      union

      select cp.idFk,u.idFk
      from 
      (
        select t.id as idFk, x.*
        from t cross join (select c, d from u where idFk = 1) as x
        where t.id <> 1      
      ) cp
      right join (select * from u where idFk <> 1) u using(idfk,c,d)

    ) as x

    group by idFk
    having bit_and(cpidFk is not null and uIdFk is not null)

) d on d.idFk = h.id 
order by h.id;

Output for filter ID == 1:

| ID | A | B |
--------------
|  2 | k | l |
|  5 | k | l |

From these inputs:

CREATE TABLE t
    (ID int, A varchar(1), B varchar(1));

INSERT INTO t
    (ID, A, B)
VALUES
    (1, 'k', 'l'),
    (2, 'k', 'l'),
    (3, 'k', 'l'),
    (4, 'k', 'l'),
    (5, 'k', 'l'),
    (6, 'k', 'j');


CREATE TABLE u
    (IDFK int, C varchar(1), D varchar(1));

INSERT INTO u
    (IDFK, C, D)
VALUES
    (1, 'w', 'x'),
    (1, 'y', 'z'),

    (2, 'w', 'x'),
    (2, 'y', 'z'),

    (3, 'w', 'x'),
    (3, 'y', 'z'),
    (3, 'm', 'z'),

    (4, 'w', 'x'),

    (5, 'w', 'x'),
    (5, 'y', 'z'),

    (6, 'w', 'x'),
    (6, 'y', 'z');

Explanation here: Find duplicates across multiple tables

MySQL query look a little bit convoluted as it doesn’t support FULL JOIN and it doesn’t have CTEs too. We simulate FULL JOIN by unioning the result of LEFT JOIN and RIGHT JOIN