Not null check in combination: check (foo is not null) or (bar is not null).

not_null_check_in_combination_demo.sql

DROP TABLE IF EXISTS snp_info;
CREATE TABLE snp_info (
	snp_id varchar NOT NULL,
	foo integer,
	bar integer
	CHECK (foo IS NOT NULL OR bar IS NOT NULL)
);

-- Success:
-- INSERT INTO snp_info VALUES ('rs10', 1, NULL);
-- INSERT INTO snp_info VALUES ('rs10', NULL, 1);

-- Fail:
-- INSERT INTO snp_info VALUES ('rs10', NULL, NULL);
-- INSERT INTO snp_info VALUES (NULL, NULL, NULL);