There's no built-in function that does that. However...

Itzik, in his PASS precon, showed a cool trick for faking one using some highschool maths.

LOG_x(a * b * c) = LOG_x(a) + LOG_x(b) + LOG_x(c)

So...

DECLARE @test-2 TABLE (val int)

INSERT INTO @test-2 VALUES (1)

INSERT INTO @test-2 VALUES (2)

INSERT INTO @test-2 VALUES (3)

INSERT INTO @test-2 VALUES (4)

INSERT INTO @test-2 VALUES (5)

SELECT

POWER(10., SUM(LOG10(val)))

FROM @test-2

Result: 120