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just for fun:
SELECT t0.proid, MIN(t0.prc)
FROM tt1 t0, tt1 t1
WHERE (((t0.bdate, t0.edate)overlaps(t1.bdate, t1.edate) AND t0.proid = t1.proid) OR
((t1.bdate, t1.edate) overlaps(t0.bdate, t0.edate) AND t0.proid = t1.proid))
AND t0.id <> t1.id
GROUP BY t0.proid;
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