How Can I Efficiently Get a Simple Random Sample from a MySQL Database?

How to Efficiently Retrieve Simple Random Samples from MySQL Database

In SQL, obtaining a random sample from a large dataset can be challenging. The conventional approach involves ordering rows by a random value and selecting the desired number of rows. However, this method is inefficient, as it requires costly sorting and RAND() evaluations.

For MySQL specifically, an alternative approach provides significantly improved performance. By harnessing the unique capabilities of MySQL's RAND() function, which generates uniformly distributed random numbers, we can avoid sorting altogether.

The formula is as follows:

select * from table where rand() <= ( desired sample size / total rows )

This query generates a random number for each row, with values ranging from 0 to 1. By comparing this random number to a threshold based on the desired sample size and total number of rows, we can determine whether to display the row.

This approach allows for efficient O(n) performance without the overhead of sorting. The database can quickly select the desired sample size without incurring the significant computation time of RAND() evaluations for each row or the complexity of sorting.

By leveraging the power of MySQL's rand() function, we gain the ability to retrieve simple random samples with optimal speed and efficiency.

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