限定模糊的列名(二)
ger_id from employees e join departments d on (e.manager_id=d.manager_id);
EMPLOYEE_ID MANAGER_ID
----------- ----------
101 100
102 100
104 103
105 103
106 103
4.在oracle语法中，两个表的相同列在select子句中必须加上前缀，非相同列无限制。
相同列manager_id没有加前缀，执行失败。
SQL> select employee_id,manager_id,department_name from employees,departments
2 where employees.manager_id=departments.manager_id;
select employee_id,manager_id,department_name from employees,departments
*
ERROR at line 1:
ORA-00918: column ambiguously defined
加前缀，执行成功。
SQL> select employee_id, employees.manager_id,department_name from employees,departments
2 where employees.manager_id=departments.manager_id;
EMPLOYEE_ID MANAGER_ID DEPARTMENT_NAME
----------- ---------- ------------------------------
101 100 Executive
102 100 Executive
104 103 IT
105 103 IT