Different explain plans for the same query. Why?

Hello to all,

i´m facing two different explain plans for the same simple query in Production environment and Development environment. I would like like to know, if possible, the reasons the explain plans are differents. Initially the explain plan for both Production and Development was the same. Nothing has changed in Production.

The query is:

    SELECT

      presc_m.idprescripcion,

      MAX(aut_m.COD_ORDEN_AUTORIZACION_PRESC) max_cod_aut

    FROM

      vis_presc_autorizaciones aut_m,

      vis_prescripcion presc_m

    WHERE

      aut_m.idprescripcion = presc_m.idprescripcion

    GROUP BY

      presc_m.idprescripcion;

Table "presc_m" has an index PK on (idprescripcion).