Question

OK. I have database which is made from data used in TRAVIAN game. I have 200000 rows, so I want to reduce it for Excel analysis.

x   y   village player alliance population  date
27 -41  h1      h       S       35          2009-12-23
27 -41  h1      h       S       56          2009-12-24
27 -41  h1      h       S       60          2009-12-25
27 -41  h1      h       S       89          2009-12-26

These are just some of the important atributes in table. There is a lot of other entries for each village every time when player is logged into system. So you can see the population growing per each village. I just want to write an sql statement which returns me only entry where maximum population of the village is. (for each village of course).

I wrote something like this

SELECT * 
FROM x_world
GROUP BY village
HAVING population = max(population)

In theory i want to loop over each village and search for its biggest population entry and take just that one. I want to do this for each village. This is how i will also a total number of villages.

Answer 1

Try this query using joins. It is much faster then dependant subqueries.

SELECT 
    * 
FROM x_world as xr
INNER JOIN (
        SELECT 
                x,
                MAX(population)
        FROM x_world as xr
        GROUP BY x 
) as xt ON xt.x = xr.x
GROUP BY village

Demo