JAVA J2EE 4 U

SELECT

  t1.typname AS source_type,

  t2.typname AS target_type,

  c.castcontext,

  c.castmethod

FROM

  pg_cast c

  JOIN pg_type t1 ON c.castsource = t1.oid

  JOIN pg_type t2 ON c.casttarget = t2.oid

WHERE

  t1.typname = 'varchar' AND t2.typname = 'numeric';