数据库mysql基础2
数据库基础2
引擎
mysql 从 5.5.5 开始 默认引擎 是 innodb
以前是 MyISAM
查看 引擎
show engines \G # mysql 以 分号为结尾 \G分行显示 最佳阅读体验
myisam、innodb 区别
- myisam不支持事务 表锁 支持全文索引 不支持外键 读取效率高 如果你这张表读的多那么选择 myisam 引擎 更好
- myisam只缓存索引文件 数据文件的缓存 由 操作系统来完成
- innodb 支持事务、行锁 、支持外键
指定表引擎
创建表的时候 mysql> create table test6(id int(11))engine=myisam;
alter table 表名 engine=innodb;
增删改查
插入记录
-
insert into 表名 values(值1,值2,值3,…值n);
INSERT into users VALUE('13999999999',8,'ruirui','yangyang','123456',19); #value只能插入一行 mysql> insert into users values('13888888888',1,'lijiarui','binggege','123abc',18); Query OK, 1 row affected (0.01 sec) #插入一条记录 values 支持插入多行记录 mysql> insert into users values('13888888888',2,'lijiarui','binggege','123abc',18),('13888888888',5,'lijiarui','binggege','123abc',18),('13888888888',3,'lijiarui','binggege','123abc',18),('13888888888',4,'lijiarui','binggege','123abc',18); #插入多条 Query OK, 4 rows affected (0.01 sec) Records: 4 Duplicates: 0 Warnings: 0 -
insert into 表名(字段1,字段2,…,字段n) values(值1,值2,值3,…值n);
mysql> insert into users(id,user_name,password) value(13,'haha','heiheihei'); mysql> insert into users(id,user_name,password) values(9,'张三','123abc'),(10,'lisi','6666777'),(11,'wangwu','123123'),(12,'zhao si','9999120'); -
修改表字段 为主键自增 不用每次插入数据再插入主键了
mysql> alter table test1 modify id int(11) not null primary key auto_increment;
查询
select
诸如 python中的print
mysql> select '66666' as haha; # as 这里是起个别名
mysql> select '66666';
+-------+
| 66666 |
+-------+
| 66666 |
+-------+
1 row in set (0.00 sec)
mysql> select '66666' as haha;
+-------+
| haha |
+-------+
| 66666 |
+-------+
1 row in set (0.00 sec)
查询语句 语法
select * from 表名
select 字段1,字段2,…字段n from 表名;
select 字段1[as 别名],字段2,…字段n from 表名;
mysql> select * from users;
mysql> select id,user_name,age from users;
mysql> select id,user_name as 姓名,age as 年龄 from users;
单个字段不重复 distinct
mysql> select distinct user_name as 用户名 from users;
+----------+
| 用户名 |
+----------+
| binggege |
| yangyang |
| 张三 |
| lisi |
| wangwu |
| zhaosi |
| haha |
+----------+
7 rows in set (0.00 sec)
where 条件
| 符号 | 说明 |
|---|---|
| > | 大于 |
| < | 小于 |
| = | 等于 |
| >= | 大于等于 |
| <= | 小于等于 |
| != | 不等于 |
| and | 并且 |
| or | 或者 |
| is | 是 |
| is not | 不是 |
select * from users where id<=5;
select * from users where id<=8 and age>18; #同时满足 and 左右的条件才出来结果
select * from users where id<=8 or age>18; # 满足其中一个就返回
mysql> select * from users where jiaruilee is not null; #判断 jiaruilee 不为空的
mysql> select * from users where jiaruilee is null; # jiaruilee 为空的
like
mysql> select * from stars where username like '范冰冰'; #精确查询 跟下面精确查询结果一样
mysql> select * from stars where username='范冰冰';
mysql> select * from stars where username like '%冰冰'; #匹配冰冰为结尾的
mysql> select * from stars where username like '冰冰%'; #匹配冰冰为开头的
mysql> select * from stars where username like '%冰冰%'; #匹配包含冰冰的
排序 order by
| 符号 | 说明 |
|---|---|
| asc | 升序 |
| desc | 降序 |
默认时 asc
mysql> select * from users where id<9 order by age;
mysql> select * from users where id<9 order by age asc; #上面两个效果一样
mysql> select * from users where id<9 order by age desc;#降序排列
多字段排序
mysql> select * from users where id<9 order by age desc,tel asc;
如果第一个字段已经排序好 那么第二个字段就不生效了
如果值一样 则值相同的字段按照第二个字段进行排序
mysql> select * from users where id<9 order by age desc,tel asc;
+-------------+----+-----------+-----------+----------+------+
| tel | id | jiaruilee | user_name | password | age |
+-------------+----+-----------+-----------+----------+------+
| 13999999994 | 6 | ruirui | yangyang | 123456 | 19 |
| 13999999996 | 8 | ruirui | yangyang | 123456 | 19 |
| 13888888881 | 3 | lijiarui | binggege | 123abc | 18 |
| 13888888882 | 4 | lijiarui | binggege | 123abc | 18 |
| 13888888883 | 5 | lijiarui | binggege | 123abc | 18 |
| 13888888888 | 1 | lijiarui | binggege | 123abc | 18 |
| 13888888889 | 2 | lijiarui | binggege | 123abc | 17 |
| 13999999995 | 7 | ruirui | yangyang | 123456 | 16 |
+-------------+----+-----------+-----------+----------+------+
8 rows in set (0.00 sec)
age
上面 age 里边有 两个 19 四个18 针对 两个19 age结果一样 会对 tel 进行排序
针对四个18 age 结果一样 那么会对tel进行排序
limit 限制结果集
mysql> select * from users where age>=18 limit 5; #只显示符合条件的前五条结果
+-------------+----+-----------+-----------+----------+------+
| tel | id | jiaruilee | user_name | password | age |
+-------------+----+-----------+-----------+----------+------+
| 13888888888 | 1 | lijiarui | binggege | 123abc | 18 |
| 13888888881 | 3 | lijiarui | binggege | 123abc | 18 |
| 13888888882 | 4 | lijiarui | binggege | 123abc | 18 |
| 13888888883 | 5 | lijiarui | binggege | 123abc | 18 |
| 13999999994 | 6 | ruirui | yangyang | 123456 | 19 |
+-------------+----+-----------+-----------+----------+------+
mysql> select * from users where age>=18 order by tel desc limit 5; #排序并且限制结果集
+-------------+----+-----------+-----------+----------+------+
| tel | id | jiaruilee | user_name | password | age |
+-------------+----+-----------+-----------+----------+------+
| 13999999996 | 8 | ruirui | yangyang | 123456 | 19 |
| 13999999994 | 6 | ruirui | yangyang | 123456 | 19 |
| 13888888888 | 1 | lijiarui | binggege | 123abc | 18 |
| 13888888883 | 5 | lijiarui | binggege | 123abc | 18 |
| 13888888882 | 4 | lijiarui | binggege | 123abc | 18 |
+-------------+----+-----------+-----------+----------+------+
区间结果集选择
mysql> select * from users where age>16 and age<18;
+-------------+----+-----------+-----------+----------+------+
| tel | id | jiaruilee | user_name | password | age |
+-------------+----+-----------+-----------+----------+------+
| 13888888889 | 2 | lijiarui | binggege | 123abc | 17 |
+-------------+----+-----------+-----------+----------+------+
1 row in set (0.00 sec)
mysql> select * from users where age between 16 and 18; #包含 16 也包含 18
+-------------+----+-----------+-----------+-----------+------+
| tel | id | jiaruilee | user_name | password | age |
+-------------+----+-----------+-----------+-----------+------+
| 13888888888 | 1 | lijiarui | binggege | 123abc | 18 |
| 13888888889 | 2 | lijiarui | binggege | 123abc | 17 |
| 13888888881 | 3 | lijiarui | binggege | 123abc | 18 |
| 13888888882 | 4 | lijiarui | binggege | 123abc | 18 |
| 13888888883 | 5 | lijiarui | binggege | 123abc | 18 |
| 13999999995 | 7 | ruirui | yangyang | 123456 | 16 |
| 13912345678 | 13 | NULL | haha | heiheihei | 16 |
+-------------+----+-----------+-----------+-----------+------+
7 rows in set (0.01 sec)
limit 区间结果集 选择 分页原理
select * from 表名 limit 偏移量,数量
用户想看第几页 用户决定
每页显示多少条 我们决定
第1页 偏移量 0 每页2条
2 2 2
3 4 2
4 6 2
5 8 2
6 10 2
7 12 2
（第几页-1）*每页显示的条数 = 偏移量
select * from 表名 limit 0,2; #第一页数据
统计函数 、聚合函数
- 用户总数
- 最大值
- 平均值
- 和
- 最小值
| 方法 | 说明 |
|---|---|
| count | 统计总数 |
| sum | 求和 |
| avg | 平均数 |
| max | 最大值 |
| min | 最小值 |
mysql> select count(*) as '总数' from users;
mysql> select count(id) as '总数' from users;
mysql> select sum(age) as '总和' from users;
mysql> select avg(age) as '平均值' from users;
mysql> select max(age) as '最大年龄' from users;
mysql> select min(age) as '最小年龄' from users;
分组 group by
mysql> select * from stars group by province; # 对省份进行分组 一样的结果只显示一个
mysql> select id,username,province,count(province) from stars group by province; #统计数量之后 分组显示
分组后 结果再过滤 having
mysql> select id,username,province,count(province) as res from stars group by province having res>1;
+----+----------+----------+-----+
| id | username | province | res |
+----+----------+----------+-----+
| 1 | 范冰冰 | 山东 | 2 |
| 7 | 刘亦菲 | 湖北 | 3 |
| 2 | 李冰冰 | 湖南 | 2 |
+----+----------+----------+-----+
3 rows in set (0.01 sec)
整体使用 SQL
select [字段1 [as 别名],[函数(字段2)]......字段n]
from 表名
[where where 条件]
[group by 字段]
[having 指定结果]
[order by 字段 [desc]]
[limit]
多表联合查询
- 内连接
- 左连接
- 右连接
- 子查询
内连接
1.语法一 ： select 表1.字段1 [as 别名],表n.字段 from 表1 [别名],表n where 条件;
mysql> select user.username as 用户名,order_goods.name as 商品名称 ,order_goods.buytime as 购买时间 from user,order_goods where
user.uid=order_goods.uid;
#给表起了别名 起了就得用
mysql> select u.username as 用户名,o.name as 商品名称 ,o.buytime as 购买时间 from user u,order_goods o where u.uid=o.uid;
2.语法2 select 表1.字段1 [as 别名],表n.字段 from 表1 inner join 表2 on 条件;
mysql> select u.username,o.name,o.buytime from user u inner join order_goods o on u.uid=o.uid;
+----------+------------+-----------+
| username | name | buytime |
+----------+------------+-----------+
| 闵锐 | 苹果三件套 | 123123 |
| 石阳 | 特斯拉 | 12312345 |
| 小牧 | 螺狮粉 | 123123123 |
| 昊昊 | 宠物狗 | 123456123 |
+----------+------------+-----------+
4 rows in set (0.00 sec)
左连接
select 表1.字段1 [as 别名],表n.字段 from 表1 left join 表2 on 条件; 以left join 左边的表为准
mysql> select u.username,o.name,o.buytime from user u left join order_goods o on u.uid=o.uid;
+----------+------------+-----------+
| username | name | buytime |
+----------+------------+-----------+
| 闵锐 | 苹果三件套 | 123123 |
| 石阳 | 特斯拉 | 12312345 |
| 小牧 | 螺狮粉 | 123123123 |
| 昊昊 | 宠物狗 | 123456123 |
| 旺恒 | NULL | NULL |
| 灿灿 | NULL | NULL |
+----------+------------+-----------+
6 rows in set (0.01 sec)
如果有 NULL 就显示默认值
(case when 表.字段 is null then 默认值 else 表.字段 end ) as 别名
mysql> select u.username,(case when o.name is null then '没时间买' else o.name end) as 商品名称,(case when o.buytime is null the
n '大忙人' else o.buytime end) as 购买时间 from user u left join order_goods o on u.uid=o.uid;
+----------+------------+-----------+
| username | 商品名称 | 购买时间 |
+----------+------------+-----------+
| 闵锐 | 苹果三件套 | 123123 |
| 石阳 | 特斯拉 | 12312345 |
| 小牧 | 螺狮粉 | 123123123 |
| 昊昊 | 宠物狗 | 123456123 |
| 旺恒 | 没时间买 | 大忙人 |
| 灿灿 | 没时间买 | 大忙人 |
+----------+------------+-----------+
6 rows in set (0.00 sec)
ifnull(表.字段,'默认值'),
mysql> select u.username,ifnull(o.name,'666') as 商品名称,ifnull(o.buytime,'888') as 购买时间 from user u left join order_goods
o on u.uid=o.uid;
+----------+------------+-----------+
| username | 商品名称 | 购买时间 |
+----------+------------+-----------+
| 闵锐 | 苹果三件套 | 123123 |
| 石阳 | 特斯拉 | 12312345 |
| 小牧 | 螺狮粉 | 123123123 |
| 昊昊 | 宠物狗 | 123456123 |
| 旺恒 | 666 | 888 |
| 灿灿 | 666 | 888 |
+----------+------------+-----------+
6 rows in set (0.01 sec)
右连接
select 表1.字段1 [as 别名],表n.字段 from 表1 right join 表2 on 条件; 以right join 右边的表为准
mysql> select u.username,o.name,o.buytime from user u right join order_goods o on u.uid=o.uid;
+----------+------------+-----------+
| username | name | buytime |
+----------+------------+-----------+
| 闵锐 | 苹果三件套 | 123123 |
| 石阳 | 特斯拉 | 12312345 |
| 小牧 | 螺狮粉 | 123123123 |
| 昊昊 | 宠物狗 | 123456123 |
+----------+------------+-----------+
4 rows in set (0.00 sec)
子查询 in not in = != exists not exists any all
mysql> select * from user where uid in (1,3,4,5);
+-----+----------+-------------+----------+
| uid | username | tel | password |
+-----+----------+-------------+----------+
| 1 | 闵锐 | 13888888888 | abc123 |
| 3 | 石阳 | 13666666666 | 666666 |
| 4 | 小牧 | 13555555555 | 7777777 |
| 5 | 昊昊 | 13999999999 | 999999 |
+-----+----------+-------------+----------+
4 rows in set (0.01 sec)
mysql> select * from user where uid in (select uid from order_goods);
+-----+----------+-------------+----------+
| uid | username | tel | password |
+-----+----------+-------------+----------+
| 1 | 闵锐 | 13888888888 | abc123 |
| 3 | 石阳 | 13666666666 | 666666 |
| 4 | 小牧 | 13555555555 | 7777777 |
| 5 | 昊昊 | 13999999999 | 999999 |
+-----+----------+-------------+----------+
4 rows in set (0.01 sec)
mysql> select * from user where uid not in (select uid from order_goods);
+-----+----------+-------------+----------+
| uid | username | tel | password |
+-----+----------+-------------+----------+
| 2 | 旺恒 | 13777777777 | 123456 |
| 6 | 灿灿 | 13111111111 | 111111 |
+-----+----------+-------------+----------+
2 rows in set (0.01 sec)
>any 大于子查询种某个结果的值
>all 大于子查询结果中的所有值
mysql> select * from stars where age>all(select age from stars where username in('范冰冰','李冰冰'));
+----+----------+-------------+----------+------+------+
| id | username | balance | province | age | sex |
+----+----------+-------------+----------+------+------+
| 4 | 郭德纲 | 88888888.00 | 天津 | 50 | 0 |
+----+----------+-------------+----------+------+------+
1 row in set (0.01 sec)
# 查询比范冰冰 和 李冰冰 年龄大的人的信息
mysql> select * from stars where age select * from stars where age union union all
union 会把 union all的结果去重显示 （只有一个字段 会去重 ）
使用union union all 两个表的字段数量 及类型 要一致
mysql> select uid as 序号,username as 姓名 from user union all select id,user_name from users;
+------+----------+
| 序号 | 姓名 |
+------+----------+
| 1 | 闵锐 |
| 2 | 旺恒 |
| 3 | 石阳 |
| 4 | 小牧 |
| 5 | 昊昊 |
| 6 | 灿灿 |
| 1 | binggege |
| 2 | binggege |
| 3 | binggege |
| 4 | binggege |
| 5 | binggege |
| 6 | yangyang |
| 7 | yangyang |
| 8 | yangyang |
| 9 | 张三 |
| 10 | lisi |
| 11 | wangwu |
| 12 | zhaosi |
| 13 | haha |
+------+----------+
19 rows in set (0.00 sec)
mysql> select uid as 序号,username as 姓名 from user union select id,user_name from users;
+------+----------+
| 序号 | 姓名 |
+------+----------+
| 1 | 闵锐 |
| 2 | 旺恒 |
| 3 | 石阳 |
| 4 | 小牧 |
| 5 | 昊昊 |
| 6 | 灿灿 |
| 1 | binggege |
| 2 | binggege |
| 3 | binggege |
| 4 | binggege |
| 5 | binggege |
| 6 | yangyang |
| 7 | yangyang |
| 8 | yangyang |
| 9 | 张三 |
| 10 | lisi |
| 11 | wangwu |
| 12 | zhaosi |
| 13 | haha |
| 14 | 闵锐 |
+------+----------+
20 rows in set (0.00 sec)
mysql> select uid,username from user union all select id,user_name from users;
+-----+----------+
| uid | username |
+-----+----------+
| 1 | 闵锐 |
| 2 | 旺恒 |
| 3 | 石阳 |
| 4 | 小牧 |
| 5 | 昊昊 |
| 6 | 灿灿 |
| 1 | binggege |
| 2 | binggege |
| 3 | binggege |
| 4 | binggege |
| 5 | binggege |
| 6 | yangyang |
| 7 | yangyang |
| 8 | yangyang |
| 9 | 张三 |
| 10 | lisi |
| 11 | wangwu |
| 12 | zhaosi |
| 13 | haha |
| 14 | 闵锐 |
+-----+----------+
20 rows in set (0.00 sec)
mysql> select uid from user union all select id from users;
+-----+
| uid |
+-----+
| 6 |
| 4 |
| 3 |
| 2 |
| 1 |
| 5 |
| 1 |
| 2 |
| 3 |
| 4 |
| 5 |
| 6 |
| 7 |
| 8 |
| 9 |
| 10 |
| 11 |
| 12 |
| 13 |
| 14 |
+-----+
20 rows in set (0.00 sec)
mysql> select uid from user union select id from users;
+-----+
| uid |
+-----+
| 6 |
| 4 |
| 3 |
| 2 |
| 1 |
| 5 |
| 7 |
| 8 |
| 9 |
| 10 |
| 11 |
| 12 |
| 13 |
| 14 |
+-----+
14 rows in set (0.00 sec)
mysql> select * from stars where age