MySQL sort by, then sort a selection by

Question

I extract a number of rows from my DB with a query. Let's say that the result is 120 rows. I want to order these rows by 'score'. That's easy, since every row has a field called 'score'. Next I want to order the first 20 rows of the result randomly. So: 1st order by score, then order first 20 randomly. How would I do this?

EDIT: to be clear: I want to show ALL 120 rows, just onder the first 20 of them randomly.

Thanks!

Answer 1

Let's suppose you've got all your results in a PHP array $rows , using something like this SQL:

SELECT * from `table_name` order by `score`;

It sounds like you know how to do that bit, so I omit the details. The bit you want is the following:

// Get the first 20 rows
$top_twenty = array_slice($rows, 0, 20)

// Order them randomly
shuffle($top_twenty);

// Put them back into the $rows array, with their new order
$rows = array_replace($rows, $top_twenty);

Answer 2

Have you tried shuffling the associative array obtained in the result of the SQL?

$stmt = $db->query("SELECT * FROM table ORDER BY score LIMIT 20");
$array = $stmt->fetchAll(PDO::FETCH_ASSOC);

shuffle($array);

foreach($array as $item) {
    // Do something
}

Answer 3

SET @rowNum=0;

SELECT @rowNum:=@rowNum+1 AS rowSeq,t.*
FROM tableName t
ORDER BY case  WHEN rowSeq < 20 THEN Rand() ELSE score END

Answer 4

Here is a SQL-only (well MySQL-only) solution:

SELECT *
FROM (SELECT *, @rn := @rn + 1 as rn
      FROM table cross join
           (select @rn := 0) const
      ORDER BY score
     ) t
ORDER BY (rn <= 20) desc,
         (case when rn <= 20 then rand() end),
         score;