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select emp_id,emp_wage,dept_name from employee as e inner join department as d on e.dept_id=d.dept_id where e.emp_wage>5000 group by e.emp_id;
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select dept_name,emp_id from department d left join employee e on e.dept_id=d.dept_id group by e.emp_id;
 
+------------+--------+
| dept_name  | emp_id |
+------------+--------+
| ×Éѯ²¿     | NULL   |
| Èí¼þ¿ª·¢²¿ |   1001 |
| Êг¡²ß»®²¿ |   1002 |
| ÏúÊÛ²¿     |   1003 |
| HR         |   1004 |
| HR         |   1005 |
| HR         |   1006 |
| Èí¼þ¿ª·¢²¿ |   1007 |
+------------+--------+
 
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 select dept_name from department d [inner] join employee e on d.dept_id=e.dept_id group by dept_name
 having count(e.dept_id) >=2;
 
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