MySQL数据库入门练习200句

目的：

学习总是需要记忆遗忘再记忆反反复复才能印入脑海。IT技术尤其如此。最好解决遗忘的方式，就是多多反复，然而捧起一本大部头从新看起显然效率低下。对于数据库入门级别的知识，看过一两遍，也就能理解主要机理了，欠缺在于代码练习。因此最近在重刷MySQL入门的同时，总结起来练习所使用的代码。用于以后的温习。某一天发现自己生疏了，花一点时间敲上一通，记忆就回来了。

说明：

1 大部分的语句都非常简单，进行了少量的注释;

2 代码稍有一些冗余，是为了熟练操作;

3 有意设置了一些错误，注意数据库的返回的信息;

4 所有测试在MariaDB上进行，MariaDB和MySQL几乎就是一样，但如果有错误，系手误或理解错误，望担待;

5 本文共100句代码，覆盖从数据库创建删除，表创建删除修改，键创建删除，索引创建删除的内容，后续会继续增加;

关于200句

延续我之前的MySQL入门练习100句，增加到200句，这部分主要涉及SQL语言的增删改查。比较烦琐的是查询，MySQL支持非常灵活多样的查询。这立业之涉足皮毛，但对于熟悉操作仍然有益。部分内容稍欠周详，在后续我自己练习的时候会再补上。

代码

//重建数据库
create database testdatabase;use database testdatabase;
create table tt1(id int, name varchar(20),age int,sex boolean);
show tables;desc tt1;

//插入
insert into tt1 values(1,"zhang",25,0);
insert into tt1 values(2,"wang",25,1);
select * from tt1;
insert into tt1(id,name,age,sex) values(3,"li",28,1);
insert into tt1(id,name,sex,age) values(4,"sun",0,22);
insert into tt1(id,name,sex) values(5,"zhao",30,1);
insert into tt1(id,age,name) values(6,"he",47,0);
insert into tt1(id,age,name) values(7,"chen",22,1),(7,"zhang",22,1),(7,"xie",32,1);
select * from tt1;

//修改
update tt1 set id=10,name="new",age=100,sex=0 where id=1; select * from tt1;
update tt1 set id=11,name="new" where id=2,age=25; select *from tt1;
update tt1 set id=12,sex=1 where id=7; select * from tt1;
update tt1 set sex=1 where id>3;
update tt1 set sex=0 where id<4;


//删除
delete from tt1 where id=1;select * from tt1;
delete from tt1 where id=12;select * from tt1;

//查询
alter table tt1 add address varchar(30);
update tt1 set address="Beijing" where sex=1;
update tt1 set address="Shanghai" where sex=0;
//简单查询
select id from tt1;
select id,name from tt1;
select id,name,address from tt1;
//条件查询
select id,name,address from tt1 where address="Beijing";
select * from tt1 where id in(2,3,4);
select * from tt1 where id not in(2,3,4);
select * from tt1 where id between 2 and 5;
select * from tt1 where id not between 2 and 5;
select * from tt1 where address like "beijing";
select * from tt1 where address like "bei";
select * from tt1 where address like "bei%";
select * from tt1 where address not like "bei%";
select * from tt1 where address is null;
select * from tt1 where address is not null;
select * from tt1 where age<20 and sex=1;
select * from tt1 where sex=0 or age>30;
//查询结果不重复
select distinct address from tt1;  
//查询结果排序
select * from tt1 order by age;
select * from tt1 order by age asc;
select * from tt1 order by age desc;
//分组查询
select * from tt1 group by sex;//单独使用group by 只会选择每个分组的一条记录
//group by 与 group_concat结合使用
select group_concat(name),sex from tt1 group by sex;
select group_concat(name),group_concat(age),sex from tt1 group by sex;
select group_concat(name,age),sex from tt1 group by sex;
//group by与集合函数结合使用
select sex,count(sex) from tt1 group by sex;
select sex,count(sex) from tt1 group by sex having sex>2;//having用于对分组后的结果加限制条件
select sex,count(sex) from tt1 group by sex having count(sex)>2;
//with rollup
select sex,count(sex) from tt1 group by sex with rollup;//在显示记录的最后一行加一条，记录是上面所有记录的和，通常用于合计数量
//limit显示限制
select * from tt1;
select * from tt1 limit 2;
select * from tt1 limit 3;
select * from tt1 limit 0,2;
select * from tt1 limit 1,2;
//使用集合函数查询
//为了更好的理解本问题，新建一个表
create table grade(id int,name varchar(10),subject varchar(10),score int,sex boolean);
insert into grade values(1,"wang","math",100,1),(1,"wang","english",96,1),(1,"wang","physics",90,1);
     insert into grade values(2,"li","math",96,1),(2,"li","english",85,1),(2,"li","physics",99,1);
     insert into grade values(3,"sun","math",85,0),(3,"sun","english",98,0),(3,"sun","physics",80,0);
select * from grade;
select count(*) from grade;
select id,name,sum(score) from grade where id=1;
select id,name,sun(score) from grade group by id;
select id,name,sum(score) from grade group by id order by sum(score) desc;
select id,name,avg(score) from grade where id=2;
select id,name,avg(score),sum(score) from grade where id =3;
select id,name,avg(score) from grade group by id;
select subject,avg(score) from grade group by subject;* from 
select subject,avg(score) from grade group by subject order by avg(score);
select name,max(score) from grade where subject="math";
select name,max(score) from grade where subject="english";
//连接查询
    //内连接
create table stu(id int,name varchar(10),age int,sex boolean);
insert into stu values(1,"wang",25,1),(2,"li",23,1),(3,"sun",23,0),(4,"zhou",27,1),(5,"zhang",22,0);
select id,name,age,sex,score from stu,grade where stu.id=grade.id;
select stu.id,stu.name,stu.age,stu.sex,score from stu,grade where stu.id=grade.id;
select stu.id,stu.name,stu.age,stu.sex,score from stu,grade where stu.id=grade.id and score>90;
    //外连接
select stu.id,stu.name,stu.age,stu.sex,score from stu left join grade on stu.id=grade.id;
select stu.id,stu.name,stu.age,stu,sex,score from stu right join grade on stu.id=grade.id;
insert into grade values(4,"hu","math",99,1),(5,"liu","english",97,0);
select stu.id,stu.name,stu.age,stu.sex,subject,score from stu left join grade on stu.id=grade.id;
select stu.id,stu.name,stu.age,stu.sex,subject,score from stu right join grade on stu.id=grade.id;
    //子查询
select * from stu where id in (select *from grade);
select * from grade where id in (select * from stu);
create table scholarship(level int,money int,score int);
insert into scholarship values(1,10000,90),(2,5000,85),(3,3000,80);
select id,name,score from grade where score>=(select score from scholarship where level=1);
select id,name,score from grade where score>=(select min(score) from scholarship);
    //exists子查询
select * from stu where exists (select name from grade where id=1);
select * from grade where score>any(select score from scholarship);
select * from grade where score>all(select score from scholarship);
//合并查询结果
select name from stu union select name from grade;
select name from stu union all select name from grade;
//别名
select * from scholarship s where s.level=1;
select * from scholarship s where s.money=5000;
select s.name from stu s,grade g where s.name=g.name;
select subject as su,score as sc from grade;
select * from stu where name regexp "^w";
select * from stu where name regexp "g$";
select * from stu where name regexp "^w.g$";
select * from stu where name regexp "^w..g$";
select * from stu where name regexp "[aeo]";
select * from stu where name regexp "[a-g]";