MySQL: Select N rows, but with only unique values in one column

Question

Given this data set:

ID  Name            City            Birthyear
1   Egon Spengler   New York        1957
2   Mac Taylor      New York        1955
3   Sara         


        

Answer 1

@BlaM

UPDATED just found that its good to use USING instead of ON. it will remove duplicate columns in result.

SELECT P.*, COUNT(*) AS ct
   FROM people P
   JOIN (SELECT City, MIN(Birthyear) AS Birthyear
              FROM people 
              GROUP by City) P2 USING(Birthyear, City)
   GROUP BY P.City
   ORDER BY P.Birthyear ASC 
   LIMIT 10;

ORIGINAL POST

hi, i've tried to use your updated query but i was getting wrong results until i've added extra condition to join (also extra column into join select). transfered to your query, i'am using this:

SELECT P.*, COUNT(*) AS ct
   FROM people P
   JOIN (SELECT City, MIN(Birthyear) AS Birthyear
              FROM people 
              GROUP by City) P2 ON P2.Birthyear = P.Birthyear AND P2.City = P.City
   GROUP BY P.City
   ORDER BY P.Birthyear ASC 
   LIMIT 10;

in theory you should not need last GROUP BY P.City, but i've left it there for now, just in case. will probably remove it later.