COALESCE is a SQL function that returns the first non-NULL expression among its arguments
`nvl` is a SQL function present in its vendor-specific implementation by Oracle
Standard simpler portable
"The coalesce function is used here because it is more portable than nvl or ifnull"
from question "Set default value in select statement(not use UNION statement)"
"The ansi standard function coalesce is simpler than using nvl and decode which should be obsoleted anyway"
from question "Oracle decode null date variable"
"Coalesce is more efficient than nvl as it only evaluates the second argument if the first is null whereas nvl evaluates both arguments every time"
from question "SQL Decode Null Values"
"2 however coalesce requires all arguments to be of the same data type thus being stricter than nvl which will first attempt an implicit conversion"
from question "Can NVL Function be Cascaded?"