Código SQL [-] SELECT Campo1, Campo2 FROM Tabla WHERE (@id_cliente = 'A' and Tabla.Campo1 is null) or (@id_cliente <> 'A' and Tabla.Campo1 is not null)
SELECT Campo1, Campo2 FROM Tabla WHERE (@id_cliente = 'A' and Tabla.Campo1 is null) or (@id_cliente <> 'A' and Tabla.Campo1 is not null)