RAND

Syntax

RAND(), RAND(N)

Description

Returns a random DOUBLE precision floating point value v in the range 0 <= v < 1.0. If a constant integer argument N is specified, it is used as the seed value, which produces a repeatable sequence of column values. In the following example, note that the sequences of values produced by RAND(3) is the same both places where it occurs.

Statements using the RAND() function are not safe for replication.

Practical uses

The expression to get a random integer from a given range is the following:

FLOOR(min_value + RAND() * (max_value - min_value))

RAND() is often used to read random rows from a table, as follows:

SELECT * FROM my_table ORDER BY RAND() LIMIT 10;

Note, however, that this technique should never be used on a big table. In fact, MariaDB will read all rows in the table, will generate a random value for each of them, will order them, and finally will apply the LIMIT clause.

Examples

CREATE TABLE t (i INT);

INSERT INTO t VALUES(1),(2),(3);

SELECT i, RAND() FROM t;
+------+-------------------+
| i    | RAND()            |
+------+-------------------+
|    1 | 0.255651095188829 |
|    2 | 0.833920199269355 |
|    3 |  0.40264774151393 |
+------+-------------------+

SELECT i, RAND(3) FROM t;
+------+-------------------+
| i    | RAND(3)           |
+------+-------------------+
|    1 |  0.90576975597606 |
|    2 | 0.373079058130345 |
|    3 | 0.148086053457191 |
+------+-------------------+

SELECT i, RAND() FROM t;
+------+-------------------+
| i    | RAND()            |
+------+-------------------+
|    1 | 0.511478140495232 |
|    2 | 0.349447508668012 |
|    3 | 0.212803152588013 |
+------+-------------------+

SELECT i, RAND(3) FROM t;
+------+-------------------+
| i    | RAND(3)           |
+------+-------------------+
|    1 |  0.90576975597606 |
|    2 | 0.373079058130345 |
|    3 | 0.148086053457191 |
+------+-------------------+