SELECT Horario_Grupo.clave AS Grupo, Maestros.nombre AS Maestro, Grupo.capacidad AS Capacidad, CONCAT(lun.clave, ' ', lunes.h_inicio, '-', lunes.h_fin) AS Lunes, CONCAT(mar.clave, ' ', martes.h_inicio, '-', martes.h_fin) AS Martes, CONCAT(mie.clave, ' ',miercoles.h_inicio, '-', miercoles.h_fin) AS Miercoles, CONCAT(jue.clave, ' ', jueves.h_inicio, '-', jueves.h_fin) AS Jueves, CONCAT(vie.clave, ' ', viernes.h_inicio, '-', viernes.h_fin) AS Viernes 

FROM (SELECT * FROM Salon UNION ALL SELECT NULL, NULL, NULL NULL, NULL) lun, (SELECT * FROM Salon UNION ALL SELECT NULL, NULL, NULL NULL, NULL)  mar, (SELECT * FROM Salon UNION ALL SELECT NULL, NULL, NULL NULL, NULL)  mie, (SELECT * FROM Salon UNION ALL SELECT NULL, NULL, NULL NULL, NULL)  jue, (SELECT * FROM Salon UNION ALL SELECT NULL, NULL, NULL NULL, NULL)  vie, Horario_Salon, Horario_Salon lunes, Horario_Salon martes, Horario_Salon miercoles, Horario_Salon jueves, Horario_Salon viernes, Grupo, Horario_Grupo, Maestros 

WHERE
ISNULL(lunes.id_salon, '')=ISNULL(lun.id_salon, '') AND
ISNULL(martes.id_salon, '')=ISNULL(mar.id_salon, '') AND
ISNULL(miercoles.id_salon, '')=ISNULL(mie.id_salon, '') AND
ISNULL(jueves.id_salon, '')=ISNULL(jue.id_salon, '') AND
ISNULL(viernes.id_salon, '')=ISNULL(vie.id_salon, '') AND
Horario_Grupo.id_grupo = Grupo.id_grupo AND
lunes.id_horario_salon = Horario_Grupo.lunes AND
martes.id_horario_salon = Horario_Grupo.martes AND
miercoles.id_horario_salon = Horario_Grupo.miercoles AND
jueves.id_horario_salon = Horario_Grupo.jueves AND
viernes.id_horario_salon = Horario_Grupo.viernes AND
Maestros.id_maestro = Grupo.id_maestro