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..
1. LEFT OUTER JOIN:左外关联 SELECT e.last_name, e.department_id, d.department_name FROM employees e LEFT OUTER JOIN departments d ON (e.department_id = d.department_id); 等价于 SELECT e.last_name, e.department_id, d.department_nam..
