CREATE TABLE table_name( column1 datatype contrai,

column2 datatype,

column3 datatype,

.....

columnN datatype,

PRIMARY KEY(one or more columns) );

create table classes( id int unsigned auto_increment primary key not null, name varchar(10) );

create table students( id int unsigned primary key auto_increment not null,

name varchar(20) default '',

age tinyint unsigned default 0,

height decimal(5,2),

gender enum('男','女','保密'),

cls_id int unsigned default 0 )

insert into 表名 values(...),(...)...;
例：
insert into classes values(0,'python1'),(0,'python2');
insert into 表名(列1,...) values(值1,...),(值1,...)...;
例：
insert into students(name) values('杨康'),('杨过'),('小龙女');

create table students(
    id int unsigned primary key auto_increment not null,
    name varchar(20) default '',
    age tinyint unsigned default 0,
    height decimal(5,2),
    gender enum('男','女','保密') default '保密',
    cls_id int unsigned default 0,
    is_delete bit default 0
);

create table classes (
    id int unsigned auto_increment primary key not null,
    name varchar(30) not null
);

insert into students values
(0,'小明',18,180.00,2,1,0),
(0,'小月月',18,180.00,2,2,1),
(0,'彭于晏',29,185.00,1,1,0),
(0,'刘德华',59,175.00,1,2,1),
(0,'黄蓉',38,160.00,2,1,0),
(0,'凤姐',28,150.00,4,2,1),
(0,'王祖贤',18,172.00,2,1,1),
(0,'周杰伦',36,NULL,1,1,0),
(0,'程坤',27,181.00,1,2,0),
(0,'刘亦菲',25,166.00,2,2,0),
(0,'金星',33,162.00,3,3,1),
(0,'静香',12,180.00,2,4,0),
(0,'郭靖',12,170.00,1,4,0),
(0,'周杰',34,176.00,2,5,0);

insert into classes values (0, "python_01"), (0, "python_02");

例1：查询编号大于3的学生


select * from students where id > 3;

例2：查询编号不大于4的学生


select * from students where id <= 4;

例3：查询姓名不是“黄蓉”的学生


select * from students where name != '黄蓉';

例4：查询没被删除的学生


select * from students where is_delete=0;

例5：查询编号大于3的女同学


select * from students where id > 3 and gender=0;

例6：查询编号小于4或没被删除的学生


select * from students where id < 4 or is_delete=0;

例7：查询姓黄的学生


select * from students where name like '黄%';

例8：查询姓黄并且“名”是一个字的学生


select * from students where name like '黄_';

例9：查询姓黄或叫靖的学生


select * from students where name like '黄%' or name like '%靖';

例10：查询编号是1或3或8的学生


select * from students where id in(1,3,8);

between ... and ...表示在一个连续的范围内

例11：查询编号为3至8的学生


select * from students where id between 3 and 8;

例12：查询编号是3至8的男生


select * from students where (id between 3 and 8) and gender=1;

例13：查询没有填写身高的学生


select * from students where height is null;

判非空is not null

例14：查询填写了身高的学生


select * from students where height is not null;

例15：查询填写了身高的男生


select * from students where height is not null and gender=1;

例1：查询未删除男生信息，按学号降序

select * from students where gender=1 and is_delete=0 order by id desc;
例2：查询未删除学生信息，按名称升序

select * from students where is_delete=0 order by name;
例3：显示所有的学生信息，先按照年龄从大-->小排序，当年龄相同时 按照身高从高-->矮排序

select * from students  order by age desc,height desc;

例1：查询学生总数

select count(*) from students;

例2：查询女生的编号最大值

select max(id) from students where gender=2;

例3：查询未删除的学生最小编号

select min(id) from students where is_delete=0;

例4：查询男生的总年龄

select sum(age) from students where gender=1;

-- 平均年龄
select sum(age)/count(*) from students where gender=1;

例5：查询未删除女生的编号平均值

select avg(id) from students where is_delete=0 and gender=2;

select * from students;
+----+-----------+------+--------+--------+--------+-----------+
| id | name      | age  | height | gender | cls_id | is_delete |
+----+-----------+------+--------+--------+--------+-----------+
|  1 | 小明      |   18 | 180.00 | 女     |      1 |           |
|  2 | 小月月    |   18 | 180.00 | 女     |      2 | 
         |
|  3 | 彭于晏    |   29 | 185.00 | 男     |      1 |           |
|  4 | 刘德华    |   59 | 175.00 | 男     |      2 | 
         |
|  5 | 黄蓉      |   38 | 160.00 | 女     |      1 |           |
|  6 | 凤姐      |   28 | 150.00 | 保密   |      2 | 
         |
|  7 | 王祖贤    |   18 | 172.00 | 女     |      1 | 
         |
|  8 | 周杰伦    |   36 |   NULL | 男     |      1 |           |
|  9 | 程坤      |   27 | 181.00 | 男     |      2 |           |
| 10 | 刘亦菲    |   25 | 166.00 | 女     |      2 |           |
| 11 | 金星      |   33 | 162.00 | 中性   |      3 | 
         |
| 12 | 静香      |   12 | 180.00 | 女     |      4 |           |
| 13 | 周杰      |   34 | 176.00 | 女     |      5 |           |
| 14 | 郭靖      |   12 | 170.00 | 男     |      4 |           |
+----+-----------+------+--------+--------+--------+-----------+

select gender from students group by gender;
+--------+
| gender |
+--------+
| 男     |
| 女     |
| 中性   |
| 保密   |
+--------+
根据gender字段来分组，gender字段的全部值有4个'男','女','中性','保密'，所以分为了4组 当group by单独使用时，只显示出每组的第一条记录, 所以group by单独使用时的实际意义不大

select gender from students group by gender;
+--------+
| gender |
+--------+
| 男     |
| 女     |
| 中性   |
| 保密   |
+--------+

select gender,group_concat(name) from students group by gender;
+--------+-----------------------------------------------------------+
| gender | group_concat(name)                                        |
+--------+-----------------------------------------------------------+
| 男     | 彭于晏,刘德华,周杰伦,程坤,郭靖                                 |
| 女     | 小明,小月月,黄蓉,王祖贤,刘亦菲,静香,周杰                        |
| 中性   | 金星                                                       |
| 保密   | 凤姐                                                       |
+--------+-----------------------------------------------------------+


select gender,group_concat(id) from students group by gender;
+--------+------------------+
| gender | group_concat(id) |
+--------+------------------+
| 男     | 3,4,8,9,14       |
| 女     | 1,2,5,7,10,12,13 |
| 中性   | 11               |
| 保密   | 6                |
+--------+------------------+

select gender,group_concat(age) from students group by gender;
+--------+----------------------+
| gender | group_concat(age)    |
+--------+----------------------+
| 男     | 29,59,36,27,12       |
| 女     | 18,18,38,18,25,12,34 |
| 中性   | 33                   |
| 保密   | 28                   |
+--------+----------------------+


分别统计性别为男/女的人年龄平均值
select gender,avg(age) from students group by gender;
+--------+----------+
| gender | avg(age) |
+--------+----------+
| 男     |  32.6000 |
| 女     |  23.2857 |
| 中性   |  33.0000 |
| 保密   |  28.0000 |
+--------+----------+

分别统计性别为男/女的人的个数
select gender,count(*) from students group by gender;
+--------+----------+
| gender | count(*) |
+--------+----------+
| 男     |        5 |
| 女     |        7 |
| 中性   |        1 |
| 保密   |        1 |
+--------+----------+

select gender,count(*) from students group by gender having count(*)>2;
+--------+----------+
| gender | count(*) |
+--------+----------+
| 男     |        5 |
| 女     |        7 |
+--------+----------+

select gender,count(*) from students group by gender with rollup;
+--------+----------+
| gender | count(*) |
+--------+----------+
| 男     |        5 |
| 女     |        7 |
| 中性   |        1 |
| 保密   |        1 |
| NULL   |       14 |
+--------+----------+


select gender,group_concat(age) from students group by gender with rollup;
+--------+-------------------------------------------+
| gender | group_concat(age)                         |
+--------+-------------------------------------------+
| 男     | 29,59,36,27,12                            |
| 女     | 18,18,38,18,25,12,34                      |
| 中性   | 33                                        |
| 保密   | 28                                        |
| NULL   | 29,59,36,27,12,18,18,38,18,25,12,34,33,28 |
+--------+-------------------------------------------+

例1：查询前3行男生信息

select * from students where gender=1 limit 0,3;

select * from students where is_delete=0 limit (n-1)*m,m

例1：使用内连接查询班级表与学生表

select * from students inner join classes on students.cls_id = classes.id;
例2：使用左连接查询班级表与学生表

此处使用了as为表起别名，目的是编写简单
select * from students as s left join classes as c on s.cls_id = c.id;
例3：使用右连接查询班级表与学生表

select * from students as s right join classes as c on s.cls_id = c.id;
例4：查询学生姓名及班级名称

select s.name,c.name from students as s inner join classes as c on s.cls_id = c.id;

create table areas(
    aid int primary key,
    atitle varchar(20),
    pid int
);

source areas.sql;

select count(*) from areas where pid is null;

例1：查询省的名称为“山西省”的所有城市
select city.* from areas as city
inner join areas as province on city.pid=province.aid
where province.atitle='山西省';
例2：查询市的名称为“广州市”的所有区县
select dis.* from areas as dis
inner join areas as city on city.aid=dis.pid
where city.atitle='广州市';

select * from students where age > (select avg(age) from students);

select name from classes where id in (select cls_id from students);

select * from students where (height,age) = (select max(height),max(age) from students);

SELECT select_expr [,select_expr,...] [      
      FROM tb_name
      [WHERE 条件判断]
      [GROUP BY {col_name | postion} [ASC | DESC], ...] 
      [HAVING WHERE 条件判断]
      [ORDER BY {col_name|expr|postion} [ASC | DESC], ...]
      [ LIMIT {[offset,]rowcount | row_count OFFSET offset}]
]

select distinct *
from 表名
where ....
group by ... having ...
order by ...
limit start,count

from pymysql import *

def main():
    # 创建Connection连接
    conn = connect(host='localhost',port=3306,database='jing_dong',user='root',password='mysql',charset='utf8')
    # 获得Cursor对象
    cs1 = conn.cursor()
    # 执行insert语句，并返回受影响的行数：添加一条数据
    # 增加
    count = cs1.execute('insert into goods_cates(name) values("硬盘")')
    #打印受影响的行数
    print(count)

    count = cs1.execute('insert into goods_cates(name) values("光盘")')
    print(count)

    # # 更新
    # count = cs1.execute('update goods_cates set name="机械硬盘" where name="硬盘"')
    # # 删除
    # count = cs1.execute('delete from goods_cates where id=6')

    # 提交之前的操作，如果之前已经之执行过多次的execute，那么就都进行提交
    conn.commit()

    # 关闭Cursor对象
    cs1.close()
    # 关闭Connection对象
    conn.close()

if __name__ == '__main__':
    main()

from pymysql import *

def main():
    # 创建Connection连接
    conn = connect(host='localhost',port=3306,user='root',password='mysql',database='jing_dong',charset='utf8')
    # 获得Cursor对象
    cs1 = conn.cursor()
    # 执行select语句，并返回受影响的行数：查询一条数据
    count = cs1.execute('select id,name from goods where id>=4')
    # 打印受影响的行数
    print("查询到%d条数据:" % count)

    for i in range(count):
        # 获取查询的结果
        result = cs1.fetchone()
        # 打印查询的结果
        print(result)
        # 获取查询的结果

    # 关闭Cursor对象
    cs1.close()
    conn.close()

if __name__ == '__main__':
    main()

from pymysql import *

def main():
    # 创建Connection连接
    conn = connect(host='localhost',port=3306,user='root',password='mysql',database='jing_dong',charset='utf8')
    # 获得Cursor对象
    cs1 = conn.cursor()
    # 执行select语句，并返回受影响的行数：查询一条数据
    count = cs1.execute('select id,name from goods where id>=4')
    # 打印受影响的行数
    print("查询到%d条数据:" % count)

    # for i in range(count):
    #     # 获取查询的结果
    #     result = cs1.fetchone()
    #     # 打印查询的结果
    #     print(result)
    #     # 获取查询的结果

    result = cs1.fetchall()
    print(result)

    # 关闭Cursor对象
    cs1.close()
    conn.close()

if __name__ == '__main__':
    main()

from pymysql import *

def main():

    find_name = input("请输入物品名称：")

    # 创建Connection连接
    conn = connect(host='localhost',port=3306,user='root',password='mysql',database='jing_dong',charset='utf8')
    # 获得Cursor对象
    cs1 = conn.cursor()


    # # 非安全的方式
    # # 输入 " or 1=1 or "   (双引号也要输入)
    # sql = 'select * from goods where name="%s"' % find_name
    # print("""sql===>%s<====""" % sql)
    # # 执行select语句，并返回受影响的行数：查询所有数据
    # count = cs1.execute(sql)

    # 安全的方式
    # 构造参数列表
    params = [find_name]
    # 执行select语句，并返回受影响的行数：查询所有数据
    count = cs1.execute('select * from goods where name=%s', params)
    # 注意：
    # 如果要是有多个参数，需要进行参数化
    # 那么params = [数值1, 数值2....]，此时sql语句中有多个%s即可 

    # 打印受影响的行数
    print(count)
    # 获取查询的结果
    # result = cs1.fetchone()
    result = cs1.fetchall()
    # 打印查询的结果
    print(result)
    # 关闭Cursor对象
    cs1.close()
    # 关闭Connection对象
    conn.close()

if __name__ == '__main__':
    main()

-- 选择数据库
use jing_dong;
-- 查看goods表
show create table goods;

begin;
或者
start transaction;

commit;

rollback;

step1：连接
终端1：查询商品分类信息
select * from goods_cates;
step2：增加数据
终端2：开启事务，插入数据
begin;
insert into goods_cates(name) values('小霸王游戏机');
终端2：查询数据，此时有新增的数据
select * from goods_cates;
step3：查询
终端1：查询数据，发现并没有新增的数据
select * from goods_cates;
step4：提交
终端2：完成提交
commit;
step5：查询
终端1：查询，发现有新增的数据
select * from goods_cates;

step1：连接
终端1
select * from goods_cates;
step2：增加数据
终端2：开启事务，插入数据
begin;
insert into goods_cates(name) values('小霸王游戏机');
终端2：查询数据，此时有新增的数据
select * from goods_cates;
step3：查询
终端1：查询数据，发现并没有新增的数据
select * from goods_cates;
step4：回滚
终端2：完成回滚
rollback;
step5：查询
终端1：查询数据，发现没有新增的数据
select * from goods_cates;

1.创建测试表testindex
create table test_index(title varchar(10));
2. 使用python程序（ipython也可以）通过pymsql模块 向表中加入十万条数据
from pymysql import connect

def main():
    # 创建Connection连接
    conn = connect(host='localhost',port=3306,database='jing_dong',user='root',password='mysql',charset='utf8')
    # 获得Cursor对象
    cursor = conn.cursor()
    # 插入10万次数据
    for i in range(100000):
        cursor.execute("insert into test_index values('ha-%d')" % i)
    # 提交数据
    conn.commit()

if __name__ == "__main__":
    main()
3. 查询
开启运行时间监测：
set profiling=1;
查找第1万条数据ha-99999
select * from test_index where title='ha-99999';
查看执行的时间：
show profiles;
为表title_index的title列创建索引：
create index title_index on test_index(title(10));
执行查询语句：
select * from test_index where title='ha-99999';
再次查看执行的时间
show profiles;