RAND

Declaration

RAND([N])

Description

The RAND([N]) function accepts 0 or 1 parameter (where N is called the random number seed). It returns a random floating-point number in the range [0, 1.0). To obtain a random integer in the range [i, j), you can use the expression FLOOR(I + RAND() * (j - i)).

If the parameter N is not specified, the random seed is initialized before execution, and RAND() generates random numbers based on this seed. Therefore, RAND() generates a different sequence of random numbers each time.

If the parameter N is specified, it serves as the random number seed. The behavior depends on whether N is a constant or a variable:

• If N is a constant, it is initialized as the random seed before execution. RAND(N) then 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 the function is executed. The same N value will generate 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, following the same execution rules. 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

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 (0.001 sec)