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

  1. 显示数据库: show databases;
  2. 选择数据库: use dbname;
  3. 创建数据库: create database dbname charset utf8;
  4. 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

  1. 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)

     

  2. 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)

     

  3. 修改表之减少列:

        alter table tbName 
    drop 列名称;

     

  4. 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

     

  5. 修改表之删除主键

         alter table tbName　drop primary key;

     

  6. 修改表之增加索引

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

     

  7. 修改表之删除索引

         alter table tbName drop index 索引名;

     

  8. 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

  1. 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

     

  2. 分组 group by

    一般要配合5个聚合函数使用:max,min,sum,avg,count

     

  3. 筛选 having
  4. 排序 order by
  5. 限制 limit

  6. 连接查询

    1. 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

       

    2. 右链接: right join
    3. 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:

  1. 查出最贵的商品的价格

    select max(shop_price) from ecs_goods;

     

  2. 查出最大(最新)的商品编号

    select max(goods_id) from ecs_goods;

     

  3. 查出最便宜的商品的价格

    select min(shop_price) from ecs_goods;

     

  4. 查出最旧(最小)的商品编号

    select min(goods_id) from ecs_goods;

     

  5. 查询该店所有商品的库存总量

    select sum(goods_number) from ecs_goods;

     

  6. 查询所有商品的平均价

    select avg(shop_price) from ecs_goods;

     

  7. 查询该店一共有多少种商品

    select count(*) from ecs_goods;

     

  8. 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:

  1. 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 ;

     

  2. 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

     

  3. 查询该店积压的总货款

    select sum(goods_number*shop_price) from ecs_goods;

     

  4. 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;

     

  5. 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;

     

  6. 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

     

  7. 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

  1. 按价格由高到低排序

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

     

  2. 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;

     

  3. 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;

     

  4. 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;

     

  5. 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

  1. 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;

     

  2. 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;

     

  3. 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;

     

  4. 用友面试题

6. union查询

  1. 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.
  2. 3期学员碰到的一道面试题

7. 子查询:

  1. 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);

     

  2. 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)

  3. 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);

     

  4. 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;

     

  5. 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

posted @ 2017-08-14 21:53  章三丰  阅读(191)  评论(0)  编辑  收藏  举报