select n random rows per specified group

Question

I am struggling to find an optimal solution for the following problem. Suppose I have a table \'Table\' like this:

id    name    report_id
 1    name1    1
          


        

Answer 1

Try this:

  SELECT
    id, 
    name,
    report_id
  FROM
  (
    SELECT id,
        report_id,
        name,
        CASE WHEN @name != name THEN @rn := 1 ELSE @rn := @rn + 1 END rn,
        @name:=name
     FROM (SELECT * FROM tbl ORDER BY RAND()) a,
        (SELECT @rn:=0, @name := NULL) r
     ORDER BY name
  ) s
  WHERE rn <= 10;

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