如何在MySQL中为每个组选择多行？

Question

Here is my table "puntos":

  Equipo      Liga  Puntos
---------------------------
 At. Madrid     1     68
 Espanyol       1     64
 Barcelona      1     63
 Real Madrid    1     61
 Castellón      1     48
 Murcia         2     78
 Elche          2     70
 Sevilla        2     60
 Valladolid     2     57

I just want to get two rows per different value of the attribute "Liga", the two that have the greatest values of "Puntos" group by "Liga".

So it should return something like that:

 Equipo      Liga  Puntos
---------------------------
 At. Madrid     1     68
 Espanyol       1     64
 Murcia         2     78
 Elche          2     70

I get the result with that query:

SELECT * FROM puntos GROUP BY Liga HAVING max(puntos) 
UNION
SELECT p1.Equipo, p1.Liga, max(p1.puntos) FROM puntos p1, (SELECT * FROM puntos GROUP BY Liga HAVING max(puntos) ORDER BY Liga,puntos DESC) p2
WHERE p1.Liga=p2.Liga AND p1.puntos<p2.puntos GROUP BY Liga
ORDER BY Liga,puntos DESC

But that solution that not works if the select values of column "puntos" are equal.

Is there any other way to do it for any value, equal or not?

Answer 1

First, this solution will only work if Equipo is unique across all leagues. If not - you should add equipoID and use it instead.

Now, we first select the leader of each league. Then create a union with the same select again, only using the WHERE to filter out the teams that we've already got on our first union. That will essentially give us the follower.

Here's the query:

SELECT * FROM
  (SELECT * FROM puntos ORDER BY `liga`,`puntos` DESC) `leader`
GROUP BY `liga`

UNION
SELECT * FROM
  (SELECT * FROM puntos ORDER BY `liga`,`puntos` DESC) `follower`
WHERE `follower`.`equipo` NOT IN 
  (SELECT equipo FROM
    (SELECT * FROM puntos ORDER BY `liga`,`puntos` DESC) `leader`
   GROUP BY `liga`
  )
GROUP BY `liga`
ORDER BY `liga`

Answer 2

Get the max puntos

SELECT Equipo, Liga, max(Puntos) Puntos FROM results GROUP BY Liga

Then remove the maximum by Liga from the points and get the maximum again

SELECT Equipo, Liga, max(Puntos) Puntos FROM results A 
    WHERE Puntos NOT IN 
    (SELECT max(Puntos) Puntos FROM results B 
     WHERE A.LIGA = B.LIGA 
     GROUP BY Liga)
    GROUP BY Liga

The wrap the whole select to order the columns

SELECT Equipo, Liga, Puntos
FROM
(SELECT Equipo, Liga, max(Puntos) Puntos FROM results GROUP BY Liga
UNION 
SELECT Equipo, Liga, max(Puntos) Puntos FROM results A 
WHERE Puntos NOT IN 
(SELECT max(Puntos) Puntos FROM results B 
 WHERE A.LIGA = B.LIGA
 GROUP BY Liga)
GROUP BY Liga)  T
ORDER BY Liga ASC, Puntos DESC

Check the SqlFiddle .

Answer 3

Another option is to use 9.4 User-Defined Variables :

SELECT
  `der`.`Equipo`,
  `der`.`Liga`,
  `der`.`Puntos` 
FROM (
  SELECT
    `p`.`Equipo`,
    `p`.`Liga`,
    `p`.`Puntos`,
    IF(@`prev_liga` != `p`.`Liga`,
        @`rownum` := 1,
        @`rownum` := @`rownum` + 1
    ) `rank`,
    @`prev_liga` := `p`.`Liga`
  FROM (
    SELECT
      `Equipo`,
      `Liga`,
      `Puntos`
    FROM `puntos`
    GROUP BY `Liga`, `Puntos`
    ORDER BY `Liga`, `Puntos` DESC   
  ) `p`, (SELECT
            @`rownum` := NULL,
            @`prev_liga` := 0) `r`
) `der`
WHERE `der`.`rank` <= 2
ORDER BY `der`.`Liga`, `der`.`rank`;

SQL Fiddle demo

Two teams from the same "Liga" equal "Puntos":

SELECT
  `der`.`Equipo`,
  `der`.`Liga`,
  `der`.`Puntos` 
FROM (
  SELECT
    `p`.`Equipo`,
    `p`.`Liga`,
    `p`.`Puntos`,
    IF(@`prev_liga` != `p`.`Liga`,
        @`rownum` := 1,
        @`rownum` := @`rownum` + 1
    ) `rank`,
    @`prev_liga` := `p`.`Liga`
  FROM (
    SELECT
      `Equipo`,
      `Liga`,
      `Puntos`
    FROM `puntos`
    ORDER BY `Liga`, `Puntos` DESC   
  ) `p`, (SELECT
            @`rownum` := NULL,
            @`prev_liga` := 0) `r`
) `der`
WHERE `der`.`rank` <= 2
ORDER BY `der`.`Liga`, `der`.`rank`;

SQL Fiddle demo

Answer 4

Hi there I will suggest little different approach to this problem.

SET @num := 0, @liga := 0;

SELECT Equipo, Liga, Puntos
FROM (SELECT Equipo, Liga, Puntos, @num := if(@liga = Liga, @num + 1, 1) AS rowNumber,
              @liga := Liga
      FROM (SELECT Equipo, Liga, Puntos
            FROM results
            ORDER BY Liga, Puntos DESC) t1) tx
WHERE rowNumber <= 2;

Also here is SQL Fiddle to see how it's work...

And here you can take a look at one of my previous (very similar answer)!

GL!