How to Efficiently Select Random Rows from a Large MySQL Table?

Selecting Random Rows with MySQL: A Detailed Solution

The question arises frequently about how to effectively select random rows from a large MySQL table without resorting to the ORDER BY RAND() method, which is known to be inefficient for larger datasets. To address this challenge, let's explore a viable solution:

MySQL-Based Approach:

Utilize the combination of the following SQL statements:

SET @r := (SELECT FLOOR(RAND() * (SELECT COUNT(*) FROM mytable)));
SET @sql := CONCAT('SELECT * FROM mytable LIMIT 1 OFFSET ', @r);
PREPARE stmt1 FROM @sql;
EXECUTE stmt1;

This approach involves:

• Calculating a random row number using FLOOR(RAND() * (row count)).
• Combining the random row number with an offset in a dynamic SQL query.
• Preparing and executing the constructed query.

PHP-Based Approach:

If you prefer to work with PHP, you can employ the following code snippet:

<?php
$mysqli->begin_transaction();
$result = $mysqli->query("SELECT COUNT(*) FROM mytable");
$row = $result->fetch_row();
$count = $row[0];
$offset = mt_rand(0, $count);
$result = $mysqli->query("SELECT * FROM mytable LIMIT 1 OFFSET $offset");
...
$mysqli->commit();

This approach entails:

• Retrieving the row count using a COUNT(*) query.
• Generating a random offset.
• Executing a SELECT query with the calculated offset to retrieve a single random row.

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