How to Efficiently Select a Random Row from an SQL Database?

SQL Random Row Selection: Exploring Efficient Techniques

Selecting random rows from a database table is a valuable operation for a variety of use cases. Although SQL lacks built-in functions to directly retrieve random records, several methods provide approximations.

MySQL, PostgreSQL and Microsoft SQL Server Use a similar approach:

SELECT column
FROM table
ORDER BY RAND()
LIMIT 1;

This method uses the RAND() function to assign a random value to each row and then sorts them. The LIMIT 1 clause ensures that only the highest ranked rows are returned.

IBM DB2 uses a slightly different approach, including the following steps:

SELECT column, RAND() AS IDX
FROM table
ORDER BY IDX
FETCH FIRST 1 ROWS ONLY;

In this method, use the RAND() function to generate a random index (IDX) for each row and sort it. The FETCH FIRST 1 ROWS ONLY clause limits the results to the first row, effectively providing random selection.

Oracle uses a slightly different technology:

SELECT column
FROM (
     SELECT column
     FROM table
     ORDER BY DBMS_RANDOM.VALUE
)
WHERE ROWNUM = 1;

Here, the DBMS_RANDOM.VALUE function assigns a unique random value to each row, which is then used for sorting in nested queries. The ROWNUM = 1 clause limits the results to the highest-ranked rows, resulting in a random selection.

These methods provide an efficient way to retrieve random rows from SQL tables, allowing developers to implement a variety of functions and applications that require random data sampling.

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