为指定表添加一条数据：insert into 指定表名(字段名1,字段名2,字段名3,字段名4)values(数据1,数据2,数据3,数据4);
使用MySQL语句的例子
自动插入录入时间
sql复制代码
--新建一个自动记录时间的消息表
create table test_msg(
id int primary key auto_increment comment "主键",
message longtext comment "消息",
cre_time timestamp not null default current_timestamp comment "录入时间"
)comment="记录消息的表";
-- 没有输入时间，会自动记录插入数据时系统时间
insert into test_msg(message) values("这是一个重大的新闻");
查询其他数据库的表
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--编写一个查询其他数据库数据时数据的SQL语句
select from database_name.表名;
-- 其中database_name不是当前选择的数据库
单表查询（重点）
sql复制代码
-- 新建学生表并插入相应的数据
create table student(
s_id int(10) primary key default 0 comment'用户ID',
sname varchar(10) comment'用户姓名',
sex varchar(1) comment'用户性别',
age int(3) comment'用户年龄',
s_time DateTime comment'记录时间',
s_info longtext comment'用户简介'
)engine=InnoDB default charset=utf8;
-- 查询学生表中所有数据
select * from student;
select s_id,sname,sex,age,s_time,s_info from student;
-- 查询学生姓名为张浩的信息
select * from student where sname="张浩";
select * from student where sname in("张浩");
-- 查询学生姓名,重复的不要显示
select distinct(sname) from student;
-- 查询年龄为20-40的学生信息
select * from student where age between 20 and 40;
select * from student where age>=20 and age<=40;
-- 查询以年龄进行（小到大,大到小）排序显示学生信息
-- 小到大排序：
select * from student where age order by age asc;
-- 大到小排序：
select * from student where age order by age desc;
-- 查询姓名以A开头、以A结尾、包含A、A开头并且后面跟一个字符的学生信息
-- A开头：
select * from student where sname like'A%';
-- A结尾：
select * from student where sname like'%A';
-- 包含A：
select * from student where sname like'%A%';
-- A开头并且后面跟一个字符：
select * from student where sname like'A_';
-- 查询性别不为女的学生信息
select * from student where sex not in ('女');
select * from student where sex !='女';
-- 查询年龄是22、55岁的学生信息
select * from student where age in (22,55);
select * from student where age=22 or age=55;
-- 查询年龄由小到大，在第二到第五的所有学生信息
select * from student where age order by age desc limit 1,4;
-- 查询最新的学生信息
select * from student order by s_time desc limit 1;
-- 查询相同年龄等于2的人数，并显示其姓名
select age as "年龄",count(age) as "人数",group_concat(sname)
from student where age group by age having count(age)=2;
-- 根据学生的年龄查询显示学生处于的年龄段
select * ,
case when t1.age between 0 and 18 then 'young'
when t1.age between 19 and 45 then 'middle'
else 'old' end as 'test_age'
from student t1;
-- 将李丽的年龄更新100岁
update student set sex='女',age="100" where s_id='97';
-- 删除李丽的数据
delete from student where sname="李丽";
-- 清除学生表所有的数据
truncate table student;
左连接查询 ：left join 表名 on 连接条件......-----左表全部保留，右表关联不上用null表示；
右连接查询 ：right join 表名 on 连接条件......-----右表全部保留，左表关联不上的用null表示；
内连接查询 ：inner join 表名 on- 连接条件（join 表名 on 连接条件）......-----两表关联保留两表中交集的记录；
全连接查询 ：左连接+ union all +右连接-----两表关联查询它们的所有记录；
三表查询（重点)
sql复制代码
-- 创建员工表
create table employee(
id int primary key auto_increment,
name varchar(10) unique,
age int,
salary double,
check(salary>7000 and salary<=15000),
relation_department_name varchar(20));
-- 创建部门表
create table department(
id int primary key auto_increment,
department_name varchar(20) unique,
department_person_num int);
-- 创建项目表
create table project(
id int primary key auto_increment,
project_name varchar(20),
relation_department_name varchar(20));
-- 1、要求-查询姓名为张三的员工，所在部门的名称、部门人数、关联项目的数量、关联项目的具体名称
select t1.name as "姓名", t2.department_name as "部门名",
t2.department_person_num as "部门人数",count(t3.project_name) as "关联项目个数",
group_concat(t3.project_name) as "关联项目名称"
from employee t1, department t2, project t3
where t1.relation_department_name = t2.department_name
and t2.department_name = t3.relation_department_name
and t1.name = "张三" group by t2.department_name,t2.department_person_num ;
select t1.name as "姓名",t2.department_name as "部门名", t2.department_person_num as "部门人数",
count(t3.project_name) as "关联项目个数",group_concat(t3.project_name) as "关联项目名称"
from employee t1 left join department t2 on t1.relation_department_name = t2.department_name
left join project t3 on t2.department_name = t3.relation_department_name
where t2.department_name is not null
and t3.relation_department_name is not null
and t1.name = "张三" group by t2.department_name,t2.department_person_num ;
-- 2、要求-查询所有的员工，所在部门的人数与关联的项目数，具体项目的名称？
select t1.name as "姓名",t2.department_person_num as "部门人数",
count(t3.project_name) as "关联项目个数",group_concat(t3.project_name) as "关联项目名称"
from employee t1, department t2, project t3
where t1.relation_department_name = t2.department_name
and t2.department_name = t3.relation_department_name
group by t1.name,t2.department_person_num ;
select t1.name as "姓名",t2.department_person_num as "部门人数",
count(t3.project_name) as "关联项目个数",group_concat(t3.project_name) as "关联项目名称"
from employee t1 left join department t2 on t1.relation_department_name = t2.department_name
left join project t3 on t2.department_name = t3.relation_department_name
where t2.department_name is not null
and t3.relation_department_name is not null
group by t1.name,t2.department_person_num ;
-- 3、要求-查询出每个人工程师所在的部门、薪资、负责项目名称
select t1.name as "姓名",t2.department_name as "部门名",t1.salary as "薪资",
group_concat(t3.project_name) as "关联项目名称"
from employee t1, department t2, project t3
where t1.relation_department_name = t2.department_name
and t2.department_name = t3.relation_department_name
group by t1.name,t1.salary;
select t1.name as "姓名",t2.department_name as "部门名",t1.salary as "薪资",
group_concat(t3.project_name) as "关联项目名称"
from employee t1 left join department t2 on t1.relation_department_name = t2.department_name
left join project t3 on t2.department_name = t3.relation_department_name
where t2.department_name is not null
and t3.relation_department_name is not null
group by t1.name,t1.salary;
-- 4、要求-查询出每个人工程师所在的部门、薪资、负责项目名称，并增加一个工资阶段财富类型字段
select t1.name as "姓名",t2.department_name as "部门名",t1.salary as "薪资",
group_concat(t3.project_name) as "关联项目名称",
case when t1.salary between 0 and 4000 then "低收入"
when t1.salary between 4001 and 8000 then "中收入"
else "高收入" end as "财富类型"
from employee t1, department t2, project t3
where t1.relation_department_name = t2.department_name
and t2.department_name = t3.relation_department_name
group by t1.name,t1.salary;
select t1.name as "姓名",t2.department_name as "部门名",t1.salary as "薪资",
group_concat(t3.project_name) as "关联项目名称" ,
case when t1.salary between 0 and 4000 then "低收入"
when t1.salary between 4001 and 8000 then "中收入"
else "高收入" end as "财富类型"
from employee t1 left join department t2 on t1.relation_department_name = t2.department_name
left join project t3 on t2.department_name = t3.relation_department_name
where t2.department_name is not null
and t3.relation_department_name is not null
group by t1.name,t1.salary;
-- 5、要求-查询项目中学生管理系统最高薪资的工程师姓名、所在项目、薪资
select t1.name as "姓名",t3.project_name as "项目名",t1.salary as "薪资"
from employee t1, department t2, project t3
where t1.relation_department_name = t2.department_name
and t2.department_name = t3.relation_department_name
and t3.project_name = "学生管理系统"
order by t1.salary desc limit 1;
select t1.name as "姓名",t3.project_name as "项目名",t1.salary as "薪资"
from employee t1 left join department t2 on t1.relation_department_name = t2.department_name
left join project t3 on t2.department_name = t3.relation_department_name
where t2.department_name is not null
and t3.relation_department_name is not null
and t3.project_name = "学生管理系统"
order by t1.salary desc limit 1;
-- 例子如下：
-- 新建存储过程test_add：
create procedure test_add(in a int,in b int,out c int)
begin
set c=a+b;
end
-- 调用存储过程：
call test_add(2,3,@a);
-- 查看输出
select @a;
-- 删除存储过程：
drop procedure test_add;
MySQL 数据库导入导出
将表导出:
sql复制代码
-- 将表test_csv导出到指定路径下面,导成csv类型文件
select id,name from test_csv
into outfile 'D:/test_as/test(utf8).csv'
character set utf8
fields terminated by ',';
-- 导入前可以先查看导入的路径：show variables like 'secure_file_priv';
-- 将into outfile 'D:/test_as/test(utf8).csv'中路径改为对应路径
-- character set utf8 表示字符编码为utf-8
-- fields terminated by ','; 表明数据与数据直接用','分隔开
将表导入:
sql复制代码
load data local infile 'D:/test_as/test(utf8).csv'
into table test_csv
character set utf8
fields terminated by ',';
-- 将infile 'D:/test_as/test(utf8).csv'中路径改为对应路径
-- character set utf8 表示字符编码为utf-8
-- fields terminated by ','; 表明数据与数据直接用','分隔开
