combining 3 tables where combination of 2 columns is not unique

Question

There are 3 (will be up to 6 in the future) tables with the same columns.

I need to unify them, i.e. union on same columns. In addition to this - rows shall not be unique, based on 2 column combination! There are a couple of examples on the net, but all of them show how to exclude unique column values based on WHERE for one column. In my case there are 2 columns (Col1 and Col2 combination).

Here are the schematics:

and

And here is how I imagined final query (for 3-tables) would look like:

SELECT
*
FROM
(
SELECT * FROM table1
UNION
SELECT * FROM table2
UNION
SELECT * FROM table3
)
GROUP BY
Col1, Col2
HAVING
COUNT (*) > 1

What would be a correct way?

P.S. FYI single-column solutions

Multiple NOT distinct

How to select non "unique" rows

How to Select Every Row Where Column Value is NOT Distinct

EDIT:

I have used the code from accepted answer and added additional search criteria:

  ON (SOUNDEX(Merged.[name_t1]) = SOUNDEX(Multiples.[name_t1]) OR Merged.[name_t1] LIKE '%' + Multiples.[name_t1] + '%' OR Multiples.[name_t1] LIKE '%' + Merged.[name_t1] + '%')
  AND (SOUNDEX(Merged.[name_t2]) = SOUNDEX(Multiples.[name_t2]) OR Merged.[name_t2] LIKE '%' + Multiples.[name_t2] + '%' OR Multiples.[name_t2] LIKE '%' + Merged.[name_t2] + '%')

search col1 and col2:

-by SOUNDEX

-by col1 like (col1 from other table)

-by (col1 from other table) like col1

Answer 1

Here's the basics of a CTE-based approach :

With Merged AS
(  -- CTE 1 : All Data in one table
 SELECT * FROM table1
  UNION ALL
 SELECT * FROM table2
  UNION ALL
 SELECT * FROM table3
) 
, Multiples AS
(  -- CTE 2 : Group by the fields in common
 SELECT   Col1, Col2
 FROM Merged
 GROUP BY Col1, Col2
 HAVING Count(*)>1 -- only want Groups of 2 or more
)
SELECT
  Merged.*
FROM Merged INNER JOIN Multiples
  -- Only return rows from Merged if they're in Multiples
   ON Merged.[Col1]=Multiples.[Col1]
  AND Merged.[Col2]=Multiples.[Col2]

Something like that works with my own example MS-SQL data, and it looks like SQLite syntax is the same. HTH!