Mysql复习大全（转）

基础知识:

1.数据库的连接

mysql -u -p -h

-u 用户名

-p 密码

-h host主机

2.库级知识

显示数据库: show databases;
选择数据库: use dbname;
创建数据库: create database dbname charset utf8;
删除数据库: drop database dbname;

3. 表级操作

1. 显示库下面的表

    show tables;

2. 查看表的结构:

    desc tableName;

3. 查看表的创建过程:

     show create table  tableName;

4. 创建表:

    create table tbName (

        列名称1　列类型　[列参数]　[not null default ],

        ....列2...

        ....

        列名称N　列类型　[列参数]　[not null default ]

    )engine myisam/innodb charset utf8/gbk

    例子:

    create table user (

        id int auto_increment,

        name varchar(20) not null default '',

        age tinyint unsigned not null default 0,

       index id (id)

    )engine=innodb charset=utf8;

    注:innodb是表引擎,也可以是myisam或其他,但最常用的是myisam和innodb,charset 常用的有utf8,gbk;

5. 修改表

修改表之增加列:

     alter table tbName

     add 列名称１　列类型　[列参数]　[not null default ]　#(add之后的旧列名之后的语法和创建表时的列声明一样)

修改表之修改列

     alter table tbName

    change 旧列名  新列名  列类型　[列参数]　[not null default ]

(注:旧列名之后的语法和创建表时的列声明一样)

修改表之减少列:

    alter table tbName

    drop 列名称;

修改表之增加主键

     alter table tbName add primary key(主键所在列名);

    例:alter table goods add primary key(id)

    该例是把主键建立在id列上

修改表之删除主键

     alter table tbName　drop primary key;

修改表之增加索引

     alter table tbName add [unique|fulltext] index 索引名(列名);

修改表之删除索引

     alter table tbName drop index 索引名;

清空表的数据
```
     truncate tableName;
```

4. 列类型讲解

整型:

tinyint (0~255/-128~127)

smallint (0~65535/-32768~32767)

mediumint

int

bigint (参考手册11.2)

参数解释:

    unsigned 无符号(不能为负)  zerofill 0填充  M 填充后的宽度

举例:tinyint unsigned;

    tinyint(6) zerofill;

数值型

浮点型:float double

格式:float(M,D)  unsigned\zerofill;

字符型
```
char(m) 定长

varchar(m)变长

text
```

列                   实存字符i                     实占空间                     利用率

char(M)          0<=i<=M                        M                        i/m<=100%

varchar(M)      0<=i<=M                     i+1,2                    i/i+1/2<100%

日期时间类型

year       YYYY 范围:1901~2155. 可输入值2位和4位(如98,2012)

date       YYYY-MM-DD 如:2010-03-14

time       HH:MM:SS 如:19:26:32

datetime   YYYY-MM-DD  HH:MM:SS 如:2010-03-14 19:26:32

timestamp  YYYY-MM-DD  HH:MM:SS 特性:不用赋值,该列会为自己赋当前的具体时间

5. 增删改查基本操作

1. 插入数据

-- 插入指定列

    insert into 表名(col1,col2,……) values(val1,val2……); 

-- 插入所有列

    insert into 表名 values (,,,,); 

-- 一次插入多行

    insert into 表名 values

    (val1,val2……),

    (val1,val2……),

2. 修改数据

update tablename

set

col1=newval1,

col2=newval2,

...

...

colN=newvalN

where 条件;

3. 删除数据

delete from tablenaeme where 条件;

4. select 查询

条件查询 where

a. 条件表达式的意义，表达式为真，则该行取出

b. 比较运算符  = ，!=，< > <=  >=

c. like , not like ('%'匹配任意多个字符,'_'匹配任意单个字符)

    in , not in , between and

d. is null , is not null

分组 group by

一般要配合5个聚合函数使用:max,min,sum,avg,count

筛选 having
排序 order by
限制 limit

连接查询

左连接 .. left join .. on

 table A left join table B on tableA.col1 = tableB.col2 ;

 例句:

  select 列名 from table A left join table B on tableA.col1 = tableB.col2

右链接: right join
内连接: inner join

左右连接都是以在左边的表的数据为准,沿着左表查右表.
内连接是以两张表都有的共同部分数据为准,也就是左右连接的数据之交集.
7. 子查询
where 型子查询:
内层sql的返回值在where后作为条件表达式的一部分
例句: select * from tableA where colA = (select colB from tableB where …);

from 型子查询:
内层sql查询结果,作为一张表,供外层的sql语句再次查询
例句:select * from (select * from …) as tableName where ….
8. 字符集

客服端sql编码 character_set_client

服务器转化后的sql编码 character_set_connection

服务器返回给客户端的结果集编码     character_set_results

快速把以上3个变量设为相同值: set names 字符集

存储引擎 engine=1\2

1 Myisam  速度快 不支持事务 回滚

2 Innodb  速度慢 支持事务,回滚

    ①开启事务          start transaction

    ②运行sql;

    ③提交,同时生效\回滚 commit\rollback

触发器 trigger

    监视地点:表

    监视行为:增 删 改

    触发时间:after\before

    触发事件:增 删 改

创建触发器语法

    create trigger tgName

    after/before insert/delete/update

    on tableName

    for each row

    sql; -- 触发语句

  删除触发器:drop trigger tgName;

 索引

 提高查询速度,但是降低了增删改的速度,所以使用索引时,要综合考虑.

 索引不是越多越好,一般我们在常出现于条件表达式中的列加索引.

 值越分散的列，索引的效果越好

 索引类型

 primary key主键索引

 index 普通索引

 unique index 唯一性索引

 fulltext index 全文索引

查询知识

注:以下查询基于ecshop网站的商品表(ecs_goods)
在练习时可以只取部分列,方便查看.

1. 基础查询 where的练习:

查出满足以下条件的商品
1. 主键为32的商品

select goods_id,goods_name,shop_price

 from ecs_goods

 where goods_id=32;

2. 不属第3栏目的所有商品

select goods_id,cat_id,goods_name,shop_price  from ecs_goods

 where cat_id!=3;

3. 本店价格高于3000元的商品

select goods_id,cat_id,goods_name,shop_price  from ecs_goods

 where shop_price >3000;

4. 本店价格低于或等于100元的商品

select goods_id,cat_id,goods_name,shop_price  from ecs_goods where shop_price <=100;

5. 取出第4栏目或第11栏目的商品(不许用or)

 select goods_id,cat_id,goods_name,shop_price  from ecs_goods

 where cat_id in (4,11);

6. 取出100<=价格<=500的商品(不许用and)

select goods_id,cat_id,goods_name,shop_price  from ecs_goods

 where shop_price between 100 and 500;

7. 取出不属于第3栏目且不属于第11栏目的商品(and,或not in分别实现)

select goods_id,cat_id,goods_name,shop_price  from ecs_goods where cat_id!=3 and cat_id!=11;

select goods_id,cat_id,goods_name,shop_price  from ecs_goods where cat_id not in (3,11);

8. 取出价格大于100且小于300,或者大于4000且小于5000的商品

 select goods_id,cat_id,goods_name,shop_price  from ecs_goods where shop_price>100 and shop_price <300 or shop_price >4000 and shop_price <5000;

9. 取出第3个栏目下面价格<1000或>3000,并且点击量>5的系列商品

select goods_id,cat_id,goods_name,shop_price,click_count from ecs_goods where cat_id=3 and (shop_price <1000 or shop_price>3000) and click_count>5;

10. 取出第1个栏目下面的商品(注意:1栏目下面没商品,但其子栏目下有)

 select goods_id,cat_id,goods_name,shop_price,click_count from ecs_goods

 where cat_id in (2,3,4,5);

11. 取出名字以”诺基亚”开头的商品

select goods_id,cat_id,goods_name,shop_price  from ecs_goods     where goods_name like '诺基亚%';

12. 取出名字为”诺基亚Nxx”的手机

select goods_id,cat_id,goods_name,shop_price  from ecs_goods where goods_name like '诺基亚N__';

13. 取出名字不以”诺基亚”开头的商品

select goods_id,cat_id,goods_name,shop_price from ecs_goos

 where goods_name not like '诺基亚%';

14. 取出第3个栏目下面价格在1000到3000之间,并且点击量>5 “诺基亚”开头的系列商品

 select goods_id,cat_id,goods_name,shop_price  from ecs_goods where cat_id=3 and shop_price>1000 and shop_price <3000 and click_count>5 and goods_name like '诺基亚%';

15. 一道面试题

有如下表和数组

把num值处于[20,29]之间,改为20

num值处于[30,39]之间的,改为30

mian表

+------+

| num  |

+------+

|    3 |

|   12 |

|   15 |

|   25 |

|   23 |

|   29 |

|   34 |

|   37 |

|   32 |

|   45 |

|   48 |

|   52 |

+------+

16. 练习题:
把good表中商品名为’诺基亚xxxx’的商品,改为’HTCxxxx’,
提示:大胆的把列看成变量,参与运算,甚至调用函数来处理 .
substring(),concat()

2.分组查询group:

查出最贵的商品的价格
```
select max(shop_price) from ecs_goods;
```
查出最大(最新)的商品编号
```
select max(goods_id) from ecs_goods;
```
查出最便宜的商品的价格
```
select min(shop_price) from ecs_goods;
```
查出最旧(最小)的商品编号
```
select min(goods_id) from ecs_goods;
```

查询该店所有商品的库存总量

select sum(goods_number) from ecs_goods;

查询所有商品的平均价
```
select avg(shop_price) from ecs_goods;
```
查询该店一共有多少种商品
```
select count(*) from ecs_goods;
```

查询每个栏目下面

最贵商品价格

最低商品价格

商品平均价格

商品库存量

商品种类

提示:(5个聚合函数,sum,avg,max,min,count与group综合运用)

select cat_id,max(shop_price) from ecs_goods  group by cat_id;

3. having与group综合运用查询:

查询该店的商品比市场价所节省的价格

select goods_id,goods_name,market_price-shop_price as j  from ecs_goods ;

查询每个商品所积压的货款(提示:库存*单价)

select goods_id,goods_name,goods_number*shop_price  from ecs_goods

查询该店积压的总货款

select sum(goods_number*shop_price) from ecs_goods;

查询该店每个栏目下面积压的货款.

select cat_id,sum(goods_number*shop_price) as k from ecs_goods group by cat_id;

查询比市场价省钱200元以上的商品及该商品所省的钱(where和having分别实现)

select goods_id,goods_name,market_price-shop_price  as k from ecs_goods where market_price-shop_price >200;

select goods_id,goods_name,market_price-shop_price  as k from ecs_goods having k >200;

查询积压货款超过2W元的栏目,以及该栏目积压的货款

select cat_id,sum(goods_number*shop_price) as k from ecs_goods group by cat_id having k>20000

where-having-group综合练习题

有如下表及数据

+------+---------+-------+

| name | subject | score |

+------+---------+-------+

| 张三 | 数学    |    90 |

| 张三 | 语文    |    50 |

| 张三 | 地理    |    40 |

| 李四 | 语文    |    55 |

| 李四 | 政治    |    45 |

| 王五 | 政治    |    30 |

+------+---------+-------+

要求:查询出2门及2门以上不及格者的平均成绩

## 一种错误做法

mysql> select name,count(score<60) as k,avg(score) from stu group by name having k>=2;

+------+---+------------+

| name | k | avg(score) |

+------+---+------------+

| 张三     | 3 |    60.0000 |

| 李四     | 2 |    50.0000 |

+------+---+------------+

2 rows in set (0.00 sec)

mysql> select name,count(score<60) as k,avg(score) from stu group by name;

+------+---+------------+

| name | k | avg(score) |

+------+---+------------+

| 张三     | 3 |    60.0000 |

| 李四     | 2 |    50.0000 |

| 王五     | 1 |    30.0000 |

+------+---+------------+

3 rows in set (0.00 sec)

mysql> select name,count(score<60) as k,avg(score) from stu group by name having k>=2;

+------+---+------------+

| name | k | avg(score) |

+------+---+------------+

| 张三     | 3 |    60.0000 |

| 李四     | 2 |    50.0000 |

+------+---+------------+

2 rows in set (0.00 sec)

#加上赵六后错误暴露

mysql> insert into stu

    -> values

    -> ('赵六','A',100),

    -> ('赵六','B',99),

    -> ('赵六','C',98);

Query OK, 3 rows affected (0.05 sec)

Records: 3  Duplicates: 0  Warnings: 0

#错误显现

mysql> select name,count(score<60) as k,avg(score) from stu group by name having k>=2;

+------+---+------------+

| name | k | avg(score) |

+------+---+------------+

| 张三 | 3 |    60.0000 |

| 李四 | 2 |    50.0000 |

| 赵六 | 3 |    99.0000 |

+------+---+------------+

3 rows in set (0.00 sec)

#正确思路,先查看每个人的平均成绩

mysql> select name,avg(score) from stu group by name;

+------+------------+

| name | avg(score) |

+------+------------+

| 张三 |    60.0000 |

| 李四 |    50.0000 |

| 王五 |    30.0000 |

| 赵六 |    99.0000 |

+------+------------+

4 rows in set (0.00 sec)

mysql> # 看每个人挂科情况

mysql> select name,score < 60 from stu;

+------+------------+

| name | score < 60 |

+------+------------+

| 张三 |          0 |

| 张三 |          1 |

| 张三 |          1 |

| 李四 |          1 |

| 李四 |          1 |

| 王五 |          1 |

| 赵六 |          0 |

| 赵六 |          0 |

| 赵六 |          0 |

+------+------------+

9 rows in set (0.00 sec)

mysql> #计算每个人的挂科科目

mysql> select name,sum(score < 60) from stu group by name;

+------+-----------------+

| name | sum(score < 60) |

+------+-----------------+

| 张三 |               2 |

| 李四 |               2 |

| 王五 |               1 |

| 赵六 |               0 |

+------+-----------------+

4 rows in set (0.00 sec)

#同时计算每人的平均分

mysql> select name,sum(score < 60),avg(score) as pj from stu group by name;

+------+-----------------+---------+

| name | sum(score < 60) | pj      |

+------+-----------------+---------+

| 张三 |               2 | 60.0000 |

| 李四 |               2 | 50.0000 |

| 王五 |               1 | 30.0000 |

| 赵六 |               0 | 99.0000 |

+------+-----------------+---------+

4 rows in set (0.00 sec)

#利用having筛选挂科2门以上的.

mysql> select name,sum(score < 60) as gk ,avg(score) as pj from stu group by name having gk >=2;

+------+------+---------+

| name | gk   | pj      |

+------+------+---------+

| 张三 |    2 | 60.0000 |

| 李四 |    2 | 50.0000 |

+------+------+---------+

2 rows in set (0.00 sec)

4. order by 与 limit查询

按价格由高到低排序

select goods_id,goods_name,shop_price from ecs_goods order by shop_price desc;

按发布时间由早到晚排序

select goods_id,goods_name,add_time from ecs_goods order by add_time;

接栏目由低到高排序,栏目内部按价格由高到低排序

select goods_id,cat_id,goods_name,shop_price from ecs_goods order by cat_id ,shop_price desc;

取出价格最高的前三名商品

select goods_id,goods_name,shop_price from ecs_goods order by shop_price desc limit 3;

取出点击量前三名到前5名的商品

select goods_id,goods_name,click_count from ecs_goods order by click_count desc limit 2,3;

5. 连接查询

取出所有商品的商品名,栏目名,价格

select goods_name,cat_name,shop_price from ecs_goods left join ecs_category on ecs_goods.cat_id=ecs_category.cat_id;

取出第4个栏目下的商品的商品名,栏目名,价格

select goods_name,cat_name,shop_price from ecs_goods left join ecs_category on ecs_goods.cat_id=ecs_category.cat_id where ecs_goods.cat_id = 4;

取出第4个栏目下的商品的商品名,栏目名,与品牌名

select goods_name,cat_name,brand_name from ecs_goods left join ecs_category on ecs_goods.cat_id=ecs_category.cat_id left join ecs_brand on ecs_goods.brand_id=ecs_brand.brand_id where ecs_goods.cat_id = 4;

用友面试题

6. union查询

把ecs_comment,ecs_feedback两个表中的数据,各取出4列,并把结果集union成一个结果集.
3期学员碰到的一道面试题

7. 子查询:

查询出最新一行商品(以商品编号最大为最新,用子查询实现)

select goods_id,goods_name from ecs_goods where goods_id =(select max(goods_id) from ecs_goods);

查询出编号为19的商品的栏目名称(用左连接查询和子查询分别)

用where型子查询把ecs_goods表中的每个栏目下面最新的商品取出来

select goods_id,goods_name,cat_id from ecs_goods where goods_id in (select max(goods_id) from ecs_goods group by cat_id);

用from型子查询把ecs_goods表中的每个栏目下面最新的商品取出来

select * from (select goods_id,cat_id,goods_name from ecs_goods order by goods_id desc) as t group by cat_id;

用exists型子查询,查出所有有商品的栏目

select * from category where exists (select * from goods where goods.cat_id=category.cat_id);

创建触发器:

 CREATE  trigger tg2

after insert on ord

for each row

update goods set goods_number=goods_number-new.num where id=new.gid

CREATE trigger tg3

after delete on ord

for each row

update goods set goods_number=good_number+old.num where id=old.gid

CREATE  trigger tg4

after update on ord

for each row

update goods set goods_number=goods_number+old.num-new.num where id=old.gid

转自：http://blog.csdn.net/znyyjk/article/details/52717373