how to sum values from subquerys
You can't use the new columns that way. use a subquery to use the data to calculate
SELECT
wxe4_usern.*,(wxe4_usern.a170_score + wxe4_usern.atw_score + wxe4_usern.x100_score) as darts_total_thrown
FROM
(SELECT 
u.ID as id, 
(
    SELECT `meta_value` as user_name FROM `wxe4_usermeta` 
    WHERE `umeta_id` = u.ID AND `meta_key` = 'nickname'
) as user_name,
(
    SELECT SUM(rounds) FROM wxe4_170 WHERE user = u.ID
) as a170_score,
(
    select IF (count(*) &gt; 0, count(*)*66, 0) FROM wxe4_aroundtheworld WHERE user = u.ID
) as atw_score,
(
    select IF (count(*) &gt; 0, count(*)*100, 0) FROM wxe4_X100 WHERE user = u.ID 
) as x100_score
FROM darts.wxe4_users as u) wxe4_usern