Adding argument to SELECT statement with UNION changes record number

Question

When I add a new argument to the SELECT clause of a UNION, I get more records... how can this be? Isn't a UNION just mashing them together? Example:

EDIT: They're absolutely distinct. the code column is either "IN" or "OUT", and that's what I'm using to separate the two.

EDIT2: UNION ALL gives me 80 records, like it should, but it's odd because my two SELECT statements are absolutely distinct.

FINAL EDIT: Ultimate problem was records within one of my SELECT statements being not DISTINCT, not between the two SELECT statements. Thanks all.

-- Yields 76 records
SELECT
       f.date
     , f.code
     , f.cost
  FROM a.fact f
  WHERE f.code = 'IN'
UNION
SELECT
       f2.date
     , f2.code
     , f2.cost
  FROM a.fact2 f2
  WHERE f2.code = 'OUT'
;

-- Yields 80 records
SELECT
       f.key
     , f.date
     , f.code
     , f.cost
  FROM a.fact f
  WHERE f.code = 'IN'
UNION
SELECT
       f2.key
     , f2.date
     , f2.code
     , f2.cost
  FROM a.fact2 f2
  WHERE f2.code = 'OUT'
;

Answer 1

change UNION to UNION ALL and you should get the same results. UNION selects distinct rows, UNION ALL should select all.