In PostgreSQL, lcm() is a mathematical function that returns the least common multiple. We pass two numbers and the function returns the smallest strictly positive number that is an integral multiple of both inputs.

Example

Here’s an example to demonstrate:

SELECT lcm(20, 15);

Result:

60

Here are some more examples:

SELECT 
    lcm(200, 150),
    lcm(1, 2),
    lcm(1024, 512),
    lcm(0, 150),
    lcm(1024, 1024);

Result:

 lcm | lcm | lcm  | lcm | lcm  
-----+-----+------+-----+------
 600 |   2 | 1024 |   0 | 1024

Passing a Negative Value

The function returns a positive number regardless of whether we pass positive or negative values:

SELECT 
    lcm(200, -150),
    lcm(-200, 150),
    lcm(-200, -150);

Result:

 lcm | lcm | lcm 
-----+-----+-----
 600 | 600 | 600

Passing Zero

If either argument is zero, then zero is returned. This also applies when both are zero:

SELECT 
    lcm(0, 150),
    lcm(200, 0),
    lcm(0, 0);

Result:

 lcm | lcm | lcm 
-----+-----+-----
   0 |   0 |   0

Passing a Null Value

If any one of the arguments is null, then null is returned:

SELECT 
    lcm(null, 150),
    lcm(200, null);

Result:

 lcm  | lcm  
------+------
 null | null

But if both arguments are null, an error is returned:

SELECT lcm(null, null);

Result:

ERROR:  function lcm(unknown, unknown) is not unique
LINE 1: SELECT lcm(null, null);
               ^
HINT:  Could not choose a best candidate function. You might need to add explicit type casts.

Passing the Wrong Argument Type

If any of the arguments are not numeric, an error is returned:

SELECT lcm('cat', 150);

Result:

ERROR:  function lcm(unknown, unknown) is not unique
LINE 1: SELECT lcm(null, null);
               ^
HINT:  Could not choose a best candidate function. You might need to add explicit type casts.
barney=# SELECT lcm('cat', 150);
ERROR:  invalid input syntax for type integer: "cat"
LINE 1: SELECT lcm('cat', 150);
                   ^