Returns the first non null expression in the argument list.
If all arguments are NULL COALESCE will return NULL.
Coalesce may be used in select statements as a subquery to perform a sort of NULL replacement ability.
In this case if the COL3 contained a null it would be replaced with 0 in the returned recordset.
Returns 1 because it is the first non null expression.
Returns 2 because it is the first non null expression.