Elasticsearch SQL 支持下列比较运算符：
- 等于（=）
SELECT last_name l FROM "test_emp" WHERE emp_no = 10000 LIMIT 5;
- 不等（<> or != or <=>）
SELECT last_name l FROM "test_emp" WHERE emp_no <> 10000 ORDER BY emp_no LIMIT 5;
- 比较
SELECT last_name l FROM "test_emp" WHERE emp_no < 10003 ORDER BY emp_no LIMIT 5;
- 区间
SELECT last_name l FROM "test_emp" WHERE emp_no BETWEEN 9990 AND 10003 ORDER BY emp_no;
- 为空/不为空
SELECT last_name l FROM "test_emp" WHERE emp_no IS NOT NULL AND gender IS NULL;