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  • sql的基本语法

    一. 数据库

    1.查询服务器上有哪些数据库

    show databases;

    2.新建数据库

    create database TestSqlSugar;

    3.进入数据库

    use TestSqlSugar;

    4.删除数据库

    drop database test;

    二. 数据表

    1.新建表 

    (1) user

    create table if not exists user(
        id int auto_increment,
        userName varchar(100) not null,
        userPassword varchar(500) not null,
        age int not null,
        regTime datetime default current_timestamp,
        departmentId int,
        primary key(id)
    );

    (2) department

    create table if not exists department
    (
        id int auto_increment,
        name varchar(100) not null,
        admin varchar(100) not null,
        phone varchar(15) not null,
        primary key(id)
    );

    2.表查询

    select * from user
    select * from department
    ### 包含条件查询
    select * from user where id in (1);
    ### 分页limit temp1,temp2  调过temp1条temp2条数据
    select * from user limit 1,2
    ### 双表左关联查询,表的重命名
    select user.id as 'Id', user.departmentId as 'depId', user.userName as 'name' from user user left join department dep on(user.departmentId = dep.id)
    ### 两个Queryable的join
    select
    j1.* from (select user.id,user.userName,user.regTime,dep.name from user user inner join department dep on(user.departmentId=dep.id)) j1 inner join(select id,userName,userPassword,age,regTime,departmentId from user) j2 on(j1.id = j2.id)
    ### 三表关联查询,排序
    select user.id,user.userName,user.userPassword,user.age,user.regTime,
    user.departmentId,dep.id,dep.name,dep.admin,dep.phone,
    userInfo.Id,userInfo.UserId,userInfo.Sex from user user Left JOIN department dep on(user.departmentId = dep.id)
    Left JOIN userInfo userinfo ON(user.id = userinfo.userid) where(user.age=18 or dep.id=1 or userinfo.Sex='') order by user.regTime asc,dep.id desc;
    ###简化查询,两表关联(默认inner joinselect user.id,user.userName,dep.name from user user,department dep where (user.departmentId =dep.id)
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  • 原文地址:https://www.cnblogs.com/yxcn/p/10792057.html
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