RAND

Syntax

RAND([N])

Purpose

The RAND([N]) function returns a random floating-point number in the range [0, 1.0). You can use the expression FLOOR(I + RAND() * (j - i)) to generate a random integer in the range [i, j).

If you do not specify the N parameter, the random seed is initialized before execution. After initialization, RAND() generates random numbers based on this seed, resulting in a different sequence of random numbers each time it is executed.

If you specify the N parameter, it is used as the random seed to generate random numbers. The behavior depends on whether N is a constant or a variable:

• If N is a constant, it is used as the random seed before execution. After initialization, RAND(N) generates random numbers based on this seed. The same N value will produce the same sequence of random numbers.

• If N is a variable (such as a column value), it is used as the random seed each time it is executed. The same N value will produce the same random number.

In addition to being used in SELECT statements, RAND([N]) can also appear in WHERE, ORDER BY, and GROUP BY clauses. It follows the same execution rules as described above. For example, to randomly sort a table, you can use SELECT FROM T1 ORDER BY RAND(). To randomly sample 100 rows from a table, you can use SELECT FROM T1 ORDER BY RAND() LIMIT 100.

Examples

obclient> SELECT A, B, RAND() FROM T3;
+------+------+---------------------+
| A    | B    | RAND()              |
+------+------+---------------------+
|    1 |    1 |   0.641815407799385 |
|    2 |    2 | 0.16825051248841966 |
|    3 |    3 |  0.9158063697775886 |
+------+------+---------------------+
3 rows in set