Postgres 13

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CREATE DOMAIN uint_256 AS NUMERIC NOT NULL
CHECK (VALUE >= 0 AND VALUE < 2^256)
CHECK (SCALE(VALUE) = 0)

CREATE DOMAIN

CREATE TABLE foo (
  bar uint_256
);

CREATE TABLE

-- Should fail
INSERT INTO foo VALUES (123.4);

ERROR:  value for domain uint_256 violates check constraint "uint_256_check1"

-- Should succeed
INSERT INTO foo VALUES (123);

INSERT 0 1