MySQL Join详解

  还是先 Create table 吧
  create table emp(  id int not null primary key,  name varchar(10)  );
  create table emp_dept(  dept_id varchar(4) not null,  emp_id int not null,  emp_name varchar(10),  primary key (dept_id,emp_id));
  insert into emp() values  (1,"Dennis-1"),  (2,"Dennis-2"),  (3,"Dennis-3"),  (4,"Dennis-4"),  (5,"Dennis-5"),  (6,"Dennis-6"),  (7,"Dennis-7"),  (8,"Dennis-8"),  (9,"Dennis-9"),  (10,"Dennis-10");
  insert into emp_dept() values  ("R&D",1,"Dennis-1"),  ("DEv",2,"Dennis-2"),  ("R&D",3,"Dennis-3"),  ("Test",4,"Dennis-4"),  ("Test",5,"Dennis-5");