Question

I am having following scenario: I have a table lets say X where fields are

 -------------------------
 | City      | Country   |
 ------------------------|
 | Melbourne | Australia |
 | Phoenix   | USA       |
 | Manchester| USA       |
 | Manchester| UK        |
 | Phoenix   | USA       |
 | Pune      | India     |
 ------------------------

I am trying to update city column only when city are same and country are different. I have tried doing

UPDATE X SET (City) = CONCAT(CITY,COUNTRY) WHERE = ?

What should be where clause?

EDIT:

Output should look like

 ------------------------------
 | City           | Country   |
 -----------------------------|
 | Melbourne      | Australia |
 | Phoenix        | USA       |
 | Manchester, USA| USA       |
 | Manchester, UK | UK        |
 | Phoenix        | USA       |
 | Pune           | India     |
 ------------------------------

Answer 1

UPDATE X inner join X X_1 on X.city = X_1.city
SET X.City=CONCAT(X.city, ', ', X.Country)
WHERE X.country <> X_1.country

this sets City name to CONCAT(X.city, ', ', X.Country) only where the same City name exists in multiple countries.

EDIT: i think i prefer this other version:

UPDATE
  X inner join
  (select city from X group by city having count(*)>1) X_dup
  on X.city = X_dup.city
SET X.City=CONCAT(X.city, ', ', X.Country)

I’m using all these strange joins because MySql doesn’t allow you to update a table if you are referencing it in a subquery.