Postgres 10

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-- smallint
SELECT -32768::int2; -- fails
ERROR:  smallint out of range


-- integer
SELECT -2147483648::int4; -- fails
ERROR:  integer out of range


-- bigint
SELECT -9223372036854775808::int8; -- fails
ERROR:  bigint out of range


-- these work: :)
SELECT '-32768'::int2
     , '-2147483648'::int4
     , '-9223372036854775808'::int8;


int2
int4
int8


-32768
-2147483648
-9223372036854775808


-- Why? Operator precedence. To emphasize what happens:
-- +2147483648 is out of range, as the range is -2147483648 to 2147483647
SELECT - (2147483648::int4);
ERROR:  integer out of range