RANDOM function
The RANDOM function generates a random value between 0.0 (inclusive) and 1.0 (exclusive).
Syntax
RANDOM()
Return type
RANDOM returns a DOUBLE PRECISION number.
Usage notes
Call RANDOM after setting a seed value with the SET command to cause RANDOM to generate numbers in a predictable sequence.
Examples

Compute a random value between 0 and 99. If the random number is 0 to 1, this query produces a random number from 0 to 100:
select cast (random() * 100 as int); int4  24 (1 row)

Retrieve a uniform random sample of 10 items:
select * from sales order by random() limit 10;
Now retrieve a random sample of 10 items, but choose the items in proportion to their prices. For example, an item that is twice the price of another would be twice as likely to appear in the query results:
select * from sales order by log(1  random()) / pricepaid limit 10;

This example uses the SET command to set a SEED value so that RANDOM generates a predictable sequence of numbers.
First, return three RANDOM integers without setting the SEED value first:
select cast (random() * 100 as int); int4  6 (1 row) select cast (random() * 100 as int); int4  68 (1 row) select cast (random() * 100 as int); int4  56 (1 row)
Now, set the SEED value to
.25
, and return three more RANDOM numbers:set seed to .25; select cast (random() * 100 as int); int4  21 (1 row) select cast (random() * 100 as int); int4  79 (1 row) select cast (random() * 100 as int); int4  12 (1 row)
Finally, reset the SEED value to
.25
, and verify that RANDOM returns the same results as the previous three calls:set seed to .25; select cast (random() * 100 as int); int4  21 (1 row) select cast (random() * 100 as int); int4  79 (1 row) select cast (random() * 100 as int); int4  12 (1 row)