标签：ima select weight 顺序 技术 dep div dap src
-- SET操作符：
-- union 联合去重 两个表的字段个数和类型都得一样，起别名 应该在第一个表上操作，，排序按照第一列从小到大来排的
select employee_id, department_id from employee01 union --union all select employee_id, department_id from employee02;
minus ：取差集
-- 使两表字段个数和类型一致
select employee_id emp_id,dapartment_id,to_char(null) from employees01 union select to_number(null),department_id,department_name from departments;
--查询10,50,20部门的job_id,department_id，且department_id 按10,50,20的顺序来排列
column a_dummy noprint; select job_id,department_id,1 a_dummy from employees where department_id = 10 union select job_id,department_id,2 from employees where department_id = 50 union select job_id,department_id,3 from employees where department_id = 20 order by 3 asc;
JOB_ID DEPARTMENT_ID ---------- ------------- AD_ASST 10 SH_CLERK 50 ST_CLERK 50 ST_MAN 50 MK_MAN 20 MK_REP 20
--查询所有员工的last_name,department_id和department_name
select last_name,department_id,to_char(null) from employees union select to_char(null), department_id,department_name from departments;
标签：ima select weight 顺序 技术 dep div dap src
原文地址：https://www.cnblogs.com/afangfang/p/12564279.html
