2、非等值连接
#工资级别脚本
SELECT * FROM job_grades;

CREATE TABLE job_grades
(grade_level VARCHAR(3),
lowest_sal INT,
highest_sal INT);
INSERT INTO job_grades
VALUES (‘A’, 1000, 2999);
INSERT INTO job_grades
VALUES (‘B’, 3000, 5999);
INSERT INTO job_grades
VALUES(‘C’, 6000, 9999);
INSERT INTO job_grades
VALUES(‘D’, 10000, 14999);
INSERT INTO job_grades
VALUES(‘E’, 15000, 24999);
INSERT INTO job_grades
VALUES(‘F’, 25000, 40000);

案例1：查询员工的工资和工资级别
SELECT
salary,grade_level
FROM
employees AS e,job_grades AS j
WHERE
salary BETWEEN j.lowest_sal AND j.highest_sal;