Strange query plan

Hello!

I have following table:

CREATE TABLE table1 (
field1 INTEGER NOT NULL,
field2 INTEGER NOT NULL,
field3 CHARACTER(30),
... some more numeric fields)

I have also those indexes:

CREATE UNIQUE INDEX idx1 ON table1 USING btree (field3, field2, field1)
CREATE INDEX idx2 ON table1 USING btree (field1, field3)

Then I query this table with something like this:

SELECT SUM(...) FROM table1 WHERE field3 = 'ABC' AND field1 <> 1
GROUP BY field2

And planner picks up a sequential scan of a table. Why does he?

--
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