测试数据：city表：create table city(id int,name text);insert into city values(0,'北京'),(1,'西安'),(2,'天津'),(3,'上海'),(4,'哈尔滨'),(5,'西藏')person表：create table person(id int,lastname char(20));insert into person values(0,'T..
#案例：查询员工的工资级别SELECTsalary,grade_levelFROMemployees eJOINjob_grades gONe.`salary` BETWEEN g.`lowest_sal` AND g.`lowest_sal`;#案例：查询每个工资级别的个数，并且按级别降序SELECTCOUNT(*),grade_levelFROMjob_grades jJOINempl..
