Puedes poner varios valores reales de la columna x.c_concepto. Además prueba el select select l.c_codart, l.c_cantidad AS entrada, 0 AS salida, l.c_tlinea AS ptscompra, 0 AS ptsventa FROM lfacpro AS l, facpro AS a, articu AS z WHERE l.c_serie=a.c_serie ...