zoukankan      html  css  js  c++  java
  • 集合操作

    集合操作
    union 并集 去除重复值
    union all 也是并集 不去除重复值
    例:
    select employee_id, job_id from employees
    union all
    select employee_id, job_id from job_history;

    select employee_id, job_id from employees
    union
    select employee_id, job_id from job_history;

    intersect 交集
    select employee_id, job_id from employees
    intersect
    select employee_id, job_id from job_history;

    minus 差集
    select employee_id from employees
    minus
    select employee_id from job_history;


    select employee_id, job_id, salary from employees
    union all
    select employee_id, job_id, null from job_history;
    // 如果不能提供这个值 就用空值代替


    集合排序:
    select employee_id, job_id, salary from employees
    union all
    select employee_id, job_id, null from job_history
    order by salary;
    //order by只写一个 写在最后一个后面
    select employee_id, job_id, null from job_history
    union all
    select employee_id, job_id, salary from employees
    order by 3;
    如果没有名字就用第几列或者用别名

    DML
    insert:
    SQL> create table t1(x int, y char(1), z date);
    SQL> insert into t1(x, y, z) values (1, 'a', sysdate);
    SQL> insert into t1(x, z, y) values (2, sysdate+1, 'b');
    SQL> insert into t1(x, y, z) values (1, null, sysdate);
    SQL> insert into t1(x, z) values (2, sysdate+1);
    SQL> insert into t1 values (1, null, sysdate)
    //insert 定义列 列的声明 values 后面加列的值


    create table my_emp as select * from employees; //复制表 只复制了数据和基本结构 没有附加结构
    SQL> create table my_emp as select * from employees where 1=0;// 一张空的表 复制表结构 后面where 1=0 不可能实现所以查询的是空的


    update 更新
    SQL> update my_emp set salary=salary*1.1;
    SQL> update my_emp set salary=salary*1.1 where department_id=50;
    SQL> update my_emp set salary=salary*1.1, commission_pct=0.5 where employee_id=197;
    //定位行 更新列


    在new_dept表中删除没有员工的部门
    SQL> create table my_dept as select * from departments;
    delete from my_dept outer
    where not exists
    (select 1 from my_emp
    where department_id=outer.department_id);

    delete和truncate: delete truncate
    语句类型 dml ddl
    undo数据 产生大量undo数据 不产生undo数据
    空间管理 不释放 释放
    语法 where 删除全部数据

  • 相关阅读:
    Codeforces Round #630 (Div. 2) E. Height All the Same(组合数学 快速幂 逆元)
    Codeforces Round #627 (Div. 3) F. Maximum White Subtree(树型dp 换根法)
    Codeforces Round #630 (Div. 2) F. Independent Set (树型dp)
    权值线段树 简单总结 相关例题
    Codeforces Round #631 (Div. 2) D. Dreamoon Likes Sequences (bitmasks +dp )
    2018,奔波与意义
    geopandas overlay 函数报错问题解决方案
    使用Python实现子区域数据分类统计
    我要做数据分析
    geotrellis使用(四十二)将 Shp 文件转为 GeoJson
  • 原文地址:https://www.cnblogs.com/luo102154/p/7270496.html
Copyright © 2011-2022 走看看