MySQL select 10 random rows from 600K rows fast

Question

How can I best write a query that selects 10 rows randomly from a total of 600k?

Answer 1

From book :

Choose a Random Row Using an Offset

Still another technique that avoids problems found in the preceding alternatives is to count the rows in the data set and return a random number between 0 and the count. Then use this number as an offset when querying the data set

$rand = "SELECT ROUND(RAND() * (SELECT COUNT(*) FROM Bugs))";
$offset = $pdo->query($rand)->fetch(PDO::FETCH_ASSOC);
$sql = "SELECT * FROM Bugs LIMIT 1 OFFSET :offset";
$stmt = $pdo->prepare($sql);
$stmt->execute( $offset );
$rand_bug = $stmt->fetch();

Use this solution when you can’t assume contiguous key values and you need to make sure each row has an even chance of being selected.