Consultar numero de campos vacios

[Mithrandir]

Si lo quieres a nivel global puedes probar algo como esto:

SELECT SUM(total) as gran_total
FROM(
SELECT count(*) AS total FROM tabla WHERE foto1 IS NULL
UNION
SELECT count(*) AS total FROM tabla WHERE foto2 IS NULL
UNION
SELECT count(*) AS total FROM tabla WHERE foto3 IS NULL
) temp

Usando un CASE te sirve igual y no requieres de los subquerys:

SELECT
SUM(CASE WHEN foto1 IS NULL THEN 1 ELSE 0 END) +
SUM(CASE WHEN foto2 IS NULL THEN 1 ELSE 0 END) +
SUM(CASE WHEN foto3 IS NULL THEN 1 ELSE 0 END) AS total
FROM tabla

PD. Codigo al vuelo, probablemente haya errores de sintaxis.