change column datatype from array to integer

Question

I need to change the data type of a column from _float8 to int4

ALTER TABLE \"table\" ALTER COLUMN \"col\" SET DATA TYPE int4;

results in

Answer 1

You have to point out which element of the array should be used in the conversion, e.g.

alter table x alter column y set data type int4 using (y[1]::int)

db<>fiddle.

Answer 2

The problem is that you have an array. To fix this, you need array operators:

ALTER TABLE "table"
    ALTER COLUMN "col" SET DATA TYPE int4 USING (col[1]::integer);

Here is a db<>fiddle.