Question

I have a table with two columns:

• City
• Country

I want a result set that includes all of the City values. For the rows that the same City value I want to also include the country column. An example of my desired result set is as follows:

City
----------------
Chicago
New York
Toronto
London, Canada
London, England
Los Angeles

Note

The point of interest is the duplicate city names of “London” include a comma, space, and the country name to differentiate them.

How do I achieve this with a MySQL statement? I have tried a couple of things using group by and having clauses but I couldn’t get my desired result.

Answer 1

Use:

  SELECT a.city AS city
    FROM YOUR_TABLE a
GROUP BY a.city
  HAVING COUNT(a.country) = 1
UNION ALL
 SELECT CONCAT(b.city, ', ', b.country) AS city
   FROM YOUR_TABLE b
  WHERE EXISTS (SELECT NULL
                  FROM YOUR_TABLE c
                 WHERE c.city = b.city
              GROUP BY c.city
                HAVING COUNT(c.country) > 1)
ORDER BY city