As we know that COALESCE() function returns first non-NULL value from the list of values. The following IF-THEN-ELSE statement is equivalent to COALESCE() function.
IF value1 is not NULL THEN output = value1; ELSIF value2 is not NULL THEN output = value2; ELSIF value3 is not NULL THEN output = value3; . . . ELSIF valueN is not NULL THEN output = valueN; ELSE output = NULL; END IF;