Question

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How to request a random row in SQL?

Because of a huge table I cannot use MySQL function RAND() and trying to avoid using RAND() this way:

$a = mysql_fetch_array(mysql_query("SELECT MIN(id), MAX(id) FROM table WHERE category_id='".$var."'"));
$id = rand($a[0],$a[1]);
$id2 = rand($a[0],$a[1]);

Which doesn’t work, because: in $a I have the biggest and smallest ID with the respective category_id – that’s ok.

The problem brings the rows with $id and $id2 – because there are used the minimal and maximal ID values, but PHP function rand() will take some random value between minimum and maximum – and there is a big probability, that the picked out record will not belongs into category_id.

So I would like to ask you about a way, how could I fix this example.

THank you

Answer 1

You could try this:

$row = mysql_fetch_assoc(
    mysql_query(
      "SELECT count(*) as count FROM table WHERE category_id='$var'"));

$randomrow = rand(0, $row['count'] -1);

$q = mysql_query("
  SELECT * FROM table 
  WHERE category_id='$var'
  LIMIT 1 OFFSET $randomrow");