PostgreSQL: update tabA with a selection from tabB and tabC

I've a selection in tabC. I've applied that selection to tabB. Now I've to update tabA with values from these two selections.

SELECT on tabC and tabB:

SELECT * FROM tabC
WHERE id_field IN
  (SELECT id_field FROM tabB WHERE date_IN = '2011-02-22')
ORDER BY id_field
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UPDATE tabA:

UPDATE tabA
SET field_1 = tabC.field_1, field_2 = tabC.field_2, field_2 = tabC.field_2
FROM tabC WHERE tabA.id_field IN
  (SELECT tabC.id_field FROM tabC WHERE tabC.id_field IN
    (SELECT id_field FROM tabB WHERE date_IN = '2011-02-22'))

The UPDATE statement runs without any error but the result is not what I'd expeted: the 3 fields have the same values for all the rows. What's wrong?

---

Use inner join instead

UPDATE tabA
   SET field_1 = tabC.field_1,
       field_2 = tabC.field_2,
       field_3 = tabC.field_3 
  FROM tabC
       INNER JOIN tabB ON tabC.id_field = tabB.id_field AND tabB.date_IN = '2011-02-22'
 WHERE tabA.id_field = tabC.id_field;