How Can I Optimize MySQL's ORDER BY RAND() Function for Faster Random Row Selection?

Optimizing MySQL's ORDER BY RAND() Function for Faster Random Row Selection

MySQL's ORDER BY RAND() function is widely used for selecting random rows from a table. However, it can be inefficient, especially for large tables or frequent updates. This inefficiency is evident in slow query logs, where queries containing ORDER BY RAND() contribute significantly to the slowdown.

One potential solution is the MySQLPerformanceBlog's method, which involves splitting the query into multiple subqueries. However, this technique may not be adequate in all situations.

An Alternative Approach

An alternative approach that provides improved efficiency is shown below:

This method operates by calculating the running probability of each row being selected based on two variables. By using STRAIGHT_JOIN, the order of rows in the result is preserved, effectively providing a random selection.

Specific Case: Selecting a Single Random Record

If the requirement is to select a single random record, the following query can be used:

This query assumes an even distribution of ac_id values.

By employing these alternative approaches, you can substantially improve the performance of MySQL queries that involve the ORDER BY RAND() function.

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