сумма строк в выборке с WHERE

SELECT (`delivery`), COUNT(*) 
FROM prod_data 
WHERE `delivery` = 'Евросоюз Cream' OR `delivery` = 'Cream BetaPost' 
GROUP BY `delivery` 

Можете считать количество без группировки, фактически получится та же сумма:

SELECT COUNT(*) 
FROM prod_data 
WHERE `delivery` = 'Евросоюз Cream' OR `delivery` = 'Cream BetaPost' 

SELECT SUM(x) FROM ((
    SELECT COUNT(*) as x
    FROM prod_data 
    WHERE `delivery` = 'Евросоюз Cream' OR `delivery` = 'Cream BetaPost' 
    GROUP BY `delivery`
) as prom)

SELECT (`delivery`), COUNT(*) 
FROM prod_data   
WHERE `delivery` IN ( 'Евросоюз Cream', 'Cream BetaPost' )
GROUP BY `delivery` 
WITH ROLLUP