Usar variables dentro de consultas

[Libras]

Código SQL:

SELECT CASE WHEN variable = 1000 THEN 'OK' ELSE 'NOOK' END, variable,campo
FROM
(
SELECT SUM(tabla1.campo1 + tabla1.campo2) AS variable, SUM(tabla2.campo1) AS campo
FROM tabla1 INNER JOIN tabla2 ON tabla1.id = tabla2.id_tabla1
) t1
 

Saludos!