tkejser

  CREATE TABLE foo (x INT);
  INSERT INTO foo VALUeS (1);

  CREATE TABLE bar (x FLOAT);
  INSERT INTO bar VALUES (1);

  SELECT pg_typeof(x) FROM foo JOIN bar USING (x);

  Merge Join  (cost=338.29..931.54 rows=28815 width=4)
    Merge Cond: (bar.x = ((foo.x)::double precision))

  CREATE TABLE foo (x INT);
  INSERT INTO foo VALUeS (1);

  CREATE TABLE bar (x INT);
  INSERT INTO bar VALUES (1);

  CREATE TABLE baz (x INT);
  INSERT INTO baz VALUES (1);

  SELECT \*
  FROM foo
  JOIN bar USING (x)
  JOIN baz USING (x);

  CREATE TABLE foo (x INT);

  CREATE TABLE bar (x INT);

  SELECT \* FROM foo JOIN bar USING (x);