SELECT tle.tle_id, tle.bezeichnung, lfr.lfr_id
FROM  g1_tle tle
LEFT JOIN g1_tll tll
    ON tle.tle_id = tll.teil
LEFT JOIN g1_lfr lfr
    ON tll.lieferant = lfr.lfr_id
WHERE lfr.sperre IS NOT NULL AND

(SELECT t.lieferant
      FROM G1_TLL t, G1_LFR l
      WHERE t.lieferant = l.lfr_id AND teil = tle.tle_id AND
      (SELECT MIN(prioriaet) FROM G1_TLL t, G1_LFR l
      WHERE teil = tle.tle_id AND t.lieferant = l.lfr_id AND l.sperre IS NULL) = t.prioriaet) IS NULL