Copying data from int column to array column

Hi,

I am trying to copy the data from an integer column into an array column in
the same table. Something like this

CREATE TABLE test (field1 INT, field2 INT, field3 INT[]);

INSERT INTO test VALUES(1);
INSERT INTO test VALUES(2);
INSERT INTO test VALUES(3);
INSERT INTO test VALUES(4);
INSERT INTO test VALUES(5);

UPDATE test SET field2 = field1;
UPDATE test SET field3[1] = field1;

Why does the UPDATE of field2 work, but the UPDATE of field3 does not?

Thanks for any help

Adam

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