数据库增删改查复习

增删改查

插入数据

#插入一行
insert into student values(xwz,'男'，18);
#插入多行数据
insert into student values(xwz,'男'，18)，(jesse,'女',12);
#插入行的一部分
insert into studnet(name,gender,age) values(xwz,'男',18)
#插入查询出来的数据
insert into student(name) select name from account;

更新数据

update student set username = 'jesse' and passward = '123' where username = 'xwz';

删除数据

#delete 删除表中记录
delete from student where name = 'jesse';
#truncate 清空表数据
truncate table studnet;

查询数据

#查询单列
select username from student;
#查询多列
select username,password from student;
#查询所有列
select * from studnet;
#查询不同值
select distinct username from student;
#限制查询条件
select username from student limit 5;
select username from student limit 0,5;
select username from studnet limit 5,10;

排序

select * from student order by math_score desc, chinese_score asc;

分组

#普通分组
select name,count(age) as ages from student group by name
#分组后排序
select name,count(age) as ages from studnet group by name order by age desc;
#使用 where 和 having 过滤
select name,count(age) as ages from student where gender is not null group by name having count(*)>=1;

子查询

#子查询用于 where 子句的子查询
select name from emp where class_name operator (select class_name from class);
#用于 from 语句的子查询
select t1.name,t2.name from emp t1,(select * from class) t2 where t1.dept_id = t2.id;
#子查询的子查询
select * from student where id in (select id from studnet2 where student.id in (select id from studnet3));  

where

#select 中 where
select * from student where name = 'jesse';
#update 中 where 
update student set name = 'jesse' where name = 'xwz';
#delete 中 where
delete from student where name = 'jesse';

in 和 between

select * from student where age in (11,12,13);
select * from student where age between 11 and 13;

and 和 or 和 not

select * from student where name = 'jesse' and age = '20';
select * from student where name = 'jesse' or age = '20';
select * from studnet where name = 'jesse' not between 11 and 13;

like

select * from student where name like 'j%';
select * from student where name like '_e%';
select * from student where name like '%s%';

连接

select emp.name,dept.name from emp join dept on emp.dept_id = dept.id;
#隐式内连接
select * from emp,dept where emp.dept_id = emp.id;
#显示内连接
select * from emp inner join dept on emp.dept_id = dept.id;

组合

select * from student1
union all
select * from student2;