SELECT last_name l FROM "test_emp" WHERE emp_no = 10000 LIMIT 5;

SELECT 'elastic' <=> null AS "equals";    equals---------------false

SELECT null <=> null AS "equals";    equals---------------true

SELECT last_name l FROM "test_emp" WHERE emp_no <> 10000 ORDER BY emp_no LIMIT 5;

SELECT last_name l FROM "test_emp" WHERE emp_no < 10003 ORDER BY emp_no LIMIT 5;

SELECT last_name l FROM "test_emp" WHERE emp_no BETWEEN 9990 AND 10003 ORDER BY emp_no;

SELECT last_name l FROM "test_emp" WHERE emp_no IS NOT NULL AND gender IS NULL;

SELECT last_name l FROM "test_emp" WHERE emp_no IN (10000, 10001, 10002, 999) ORDER BY emp_no LIMIT 5;