Min(n1 [, n2 ...])
n2 (optional)
0
Evaluates the non-null occurrences of Sales_July as well as the first occurrence of Sales_August, and returns the lowest value.
The first expression evaluates the non-null occurrences of Field1 as well as the first occurrence of Field2, and returns the highest value. The final result is the minimum of the returned value compared against the values of Field3 and Field4.

Min