SELECT
total_field,
total_field + sum_anotherfield
FROM (
SELECT
SUM(table_one.field + table_two.field) AS total_field,
SUM(table_one.anotherfield) AS sum_anotherfield
FROM
table_one
JOIN
table_two ON table_one.id = table_two.id
WHERE
table_one.somefield = 1
) x