How to Multiply all values within a column with SQL like SUM()

Question

Lets say I have table with 1 column like this:

Col A
1
2
3
4

If I SUM it, then I will get this:

Col A
10
         


        

Answer 1

A quick example, supposing that the column contains only two values: a and b, both different than zero.

We are interested in x = a*b. Then, applying some math, we have:

x = a * b -> log(x) = log(a * b) -> log(x) = log(a) + log(b) ->
exp[log(x)] =  exp[log(a) + log(b)] -> x = exp[log(a) + log(b)].

Therefore:

a * b = exp[log(a) + log(b)]

This explains Matt's answer:

SELECT ROUND(EXP(SUM(LOG([Col A]))),1)

FROM your table

ROUND is required because of the limited precision of the SQL variables.