原因:①当多个表共用同一个序列时。...索引:提高查询效率
–自动创建:Oracle 会为具有唯一约束(唯一约束,主键约束)的列,自动创建索引
create table emp2(
id number(10) primary...和department_id相同的其他员工的
–employee_id, manager_id, department_id
select employee_id, manager_id, department_id...employee_id in(141, 174)
) and employee_id not in (141, 174);
select employee_id, manager_id, department_id...”
from employees;
–问题:查询员工的employee_id,last_name,要求按照员工的department_name排序
select employee_id, last_name