MySQL笔记复习(实例 全)

mysql复习

一:复习前的准备

1:确认你已安装wamp

2:确认你已安装ecshop,并且ecshop的数据库名为shop

二   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

2.1 显示数据库: show databases;

2.2 选择数据库: use dbname;

2.3 创建数据库: create database dbname charset utf8;

2.3 删除数据库: drop database dbname;

3: 表级操作:

3.1 显示库下面的表

show tables;

3.2 查看表的结构:

desc tableName;

3.3 查看表的创建过程:

show create table tableName;

3.4 创建表:

 createtable tbName (

列名称1 列类型 [列参数] [notnull default ],

....列2...

....

列名称N 列类型 [列参数] [notnull default ]

)engine myisam/innodb charset utf8/gbk

 

3.4的例子:

create table user (

    id intauto_increment,

    name varchar(20)not null default '',

    agetinyint unsigned not null default 0,

   index id (id)

   )engine=innodbcharset=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;

3.5 修改表

3.5.1   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)

3.5.2   修改表之修改列

alter table tbName

change 旧列名  新列名  列类型 [列参数] [notnull default ]

(注:旧列名之后的语法和创建表时的列声明一样)

3.5.3   修改表之减少列:

alter table tbName

drop 列名称;

3.5.4   修改表之增加主键

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

例:altertable goods add primary key(id)

该例是把主键建立在id列上

3.5.5   修改表之删除主键

alter table tbName drop primary key;

3.5.6   修改表之增加索引

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

3.5.7   修改表之删除索引

alter table tbName drop index 索引名;

3.5.8   清空表的数据

truncate tableName;

4:列类型讲解

列类型:

        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:tinyintunsigned;

            tinyint(6) zerofill;  

数值型

        浮点型:floatdouble

        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%

   

 

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

日期时间类型   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

 

5.1 插入数据

    insert into 表名(col1,col2,……)values(val1,val2……); -- 插入指定列

    insert into 表名values (,,,,); -- 插入所有列

    insert into 表名values   -- 一次插入多行

    (val1,val2……),

    (val1,val2……),

    (val1,val2……);

 

 

5.3修改数据

    update tablename

    set

   col1=newval1, 

    col2=newval2,

    ...

    ...

    colN=newvalN

    where 条件;

 

5.4,删除数据    deletefrom tablenaeme where 条件;

 

5.5,   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

 

6.1, 左连接

    .. left join ..on

    table A left jointable 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 triggertgName

    after/beforeinsert/delete/update

    on tableName

    for each row

    sql; -- 触发语句

   

  删除触发器:droptrigger 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

 

 

综合练习:

连接上数据库服务器

创建一个gbk编码的数据库

建立商品表和栏目表,字段如下:

 

商品表:goods

goods_id --主键,

goods_name -- 商品名称

cat_id  -- 栏目id

brand_id -- 品牌id

goods_sn -- 货号

goods_number -- 库存量

shop_price  -- 价格

goods_desc --商品详细描述

 

栏目表:category

cat_id --主键

cat_name -- 栏目名称

parent_id -- 栏目的父id

 

 

 

建表完成后,作以下操作:

删除goods表的goods_desc字段,及货号字段

并增加字段:click_count  -- 点击量

 

在goods_name列上加唯一性索引

在shop_price列上加普通索引

在clcik_count列上加普通索引

删除click_count列上的索引

 

 

对goods表插入以下数据:

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

| goods_id | goods_name                   | cat_id | brand_id |goods_sn  | goods_number | shop_price |click_count |

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

|        1 |KD876                        |     4 |        8 | ECS000000 |           10 |    1388.00 |           7 |

|        4 | 诺基亚N85原装充电器          |     8 |        1 | ECS000004 |           17 |      58.00 |           0 |

|        3 | 诺基亚原装5800耳机           |      8 |       1 | ECS000002 |           24|      68.00 |           3 |

|        5 | 索爱原装M2卡读卡器           |    11 |        7 | ECS000005 |            8 |      20.00 |           3 |

|        6 | 胜创KINGMAX内存卡            |     11 |       0 | ECS000006 |           15|      42.00 |           0 |

|        7 | 诺基亚N85原装立体声耳机HS-82 |      8 |        1 | ECS000007 |           20 |    100.00 |           0 |

|        8 | 飞利浦9@9v                   |      3 |       4 | ECS000008 |           17 |     399.00 |           9 |

|        9 | 诺基亚E66                    |      3 |       1 | ECS000009 |           13 |    2298.00 |          20 |

|       10 | 索爱C702c                    |      3 |       7 | ECS000010 |            7 |    1328.00 |          11 |

|       11 | 索爱C702c                    |      3 |       7 | ECS000011 |            1 |    1300.00 |           0 |

|       12 | 摩托罗拉A810                 |      3 |       2 | ECS000012 |            8|     983.00 |          14 |

|       13 | 诺基亚5320XpressMusic       |      3 |       1 | ECS000013 |            8 |    1311.00 |          13 |

|       14 | 诺基亚5800XM                 |     4 |        1 | ECS000014 |            4 |    2625.00 |           6 |

|       15 | 摩托罗拉A810                 |      3 |       2 | ECS000015 |            3|     788.00 |           8 |

|       16 | 恒基伟业G101                 |      2 |      11 | ECS000016 |            0|     823.33 |           3 |

|       17 | 夏新N7                       |      3 |       5 | ECS000017 |            1 |    2300.00 |           2 |

|       18 | 夏新T5                       |      4 |       5 | ECS000018 |            1 |    2878.00 |           0 |

|       19 | 三星SGH-F258                 |      3 |       6 | ECS000019 |            0 |     858.00 |           7 |

|       20 | 三星BC01                     |      3 |       6 | ECS000020 |           13 |     280.00 |          14 |

|       21 | 金立A30                     |      3 |      10 | ECS000021 |           40 |    2000.00 |           4 |

|       22 | 多普达TouchHD               |      3 |       3 | ECS000022 |            0 |    5999.00 |          15 |

|       23 | 诺基亚N96                    |      5 |       1 | ECS000023 |            8|    3700.00 |          17 |

|       24 |P806                         |      3 |       9 | ECS000024 |          148|    2000.00 |          36 |

|       25 | 小灵通/固话50元充值卡        |    13 |        0 | ECS000025 |            2 |      48.00 |           0 |

|       26 | 小灵通/固话20元充值卡        |    13 |        0 | ECS000026 |            2 |      19.00 |           0 |

|       27 | 联通100元充值卡              |     15 |       0 | ECS000027 |            2 |      95.00 |           0 |

|       28 | 联通50元充值卡               |     15 |       0 | ECS000028 |            0|      45.00 |           0 |

|       29 | 移动100元充值卡              |     14 |       0 | ECS000029 |            0|      90.00 |           0 |

|       30 | 移动20元充值卡               |     14 |       0 | ECS000030 |            9|      18.00 |           1 |

|       31 | 摩托罗拉E8                   |      3 |       2 | ECS000031 |            1|    1337.00 |           5 |

|       32 | 诺基亚N85                    |     3 |        1 | ECS000032 |            1 |    3010.00 |           9 |

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

 

 

 

三   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

1.1:主键为32的商品

select goods_id,goods_name,shop_price

     from ecs_goods

     wheregoods_id=32;

1.2: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;

 

1.3:本店价格高于3000元的商品

 

 selectgoods_id,cat_id,goods_name,shop_price from ecs_goods

     where shop_price>3000;

 

1.4: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;

 

1.5: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);

 

 

1.6: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_pricebetween 100 and 500;

 

 

1.7: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);

 

 

 

1.8: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 andshop_price <300 or shop_price >4000 and shop_price <5000;

 

 

 

1.9: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_countfrom ecs_goods where

cat_id=3 and (shop_price <1000 or shop_price>3000)and click_count>5;

 

1.10: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_countfrom ecs_goods

     where cat_id in(2,3,4,5);

 

1.11: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%';

 

 

1.12: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_namelike '诺基亚N__';

 

 

1.13: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_namenot like '诺基亚%';

 

1.14: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 andclick_count>5 and goods_name like '诺基亚%';

 

 

select goods_id,cat_id,goods_name,shop_price  from ecs_goods where

shop_price between 1000 and 3000 and cat_id=3  and click_count>5 and goods_name like '诺基亚%';

 

 

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 |

+------+

 

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:

2.1:查出最贵的商品的价格

select max(shop_price) from ecs_goods;

 

2.2:查出最大(最新)的商品编号

select max(goods_id) from ecs_goods;

 

2.3:查出最便宜的商品的价格

select min(shop_price) from ecs_goods;

 

2.4:查出最旧(最小)的商品编号

select min(goods_id) from ecs_goods;

 

2.5:查询该店所有商品的库存总量

select sum(goods_number) from ecs_goods;

 

2.6:查询所有商品的平均价

 selectavg(shop_price) from ecs_goods;

 

2.7:查询该店一共有多少种商品

 select count(*) fromecs_goods;

 

 

2.8: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:

3.1: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 ;

 

 

3.2: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

 

3.3:查询该店积压的总货款

select sum(goods_number*shop_price) from ecs_goods;

 

3.4: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 fromecs_goods group by cat_id;

 

3.5: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;

 

3.6: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 fromecs_goods group by cat_id

having k>20000

 

3.7: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 byname;

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

| 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 pjfrom 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

4.1:按价格由高到低排序

select goods_id,goods_name,shop_price from ecs_goods orderby shop_price desc;

 

4.2:按发布时间由早到晚排序

select goods_id,goods_name,add_time from ecs_goods order byadd_time;

 

4.3: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;

 

 

4.4:取出价格最高的前三名商品

select goods_id,goods_name,shop_price from ecs_goods orderby shop_price desc limit 3;

 

 

 

4.5: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 orderby click_count desc limit 2,3;

 

5   连接查询

5.1: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;

 

5.2: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;

 

 

 

5.3: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;

 

5.4: 用友面试题

 

根据给出的表结构按要求写出SQL语句。

Match 赛程表

 

字段名称

字段类型

描述

matchID

int

主键

hostTeamID

int

主队的ID

guestTeamID

int

客队的ID

matchResult

varchar(20)

比赛结果,如(2:0)

matchTime

date

比赛开始时间

 

 

Team 参赛队伍表

 

字段名称

字段类型

描述

teamID

int

主键

teamName

varchar(20)

队伍名称

 

 

Match的hostTeamID与guestTeamID都与Team中的teamID关联

查出2006-6-1 到2006-7-1之间举行的所有比赛,并且用以下形式列出:

拜仁  2:0 不来梅2006-6-21

 

mysql> select * from m;

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

| mid | hid  |gid  | mres | matime     |

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

|   1 |    1 |   2 | 2:0  | 2006-05-21 |

|   2 |    2 |   3 | 1:2  | 2006-06-21 |

|   3 |    3 |   1 | 2:5  | 2006-06-25 |

|   4 |    2 |   1 | 3:2  | 2006-07-21 |

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

4 rows in set (0.00 sec)

 

mysql> select * from t;

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

| tid  | tname    |

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

|    1 | 国安     |

|    2 | 申花     |

|    3 | 传智联队|

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

3 rows in set (0.00 sec)

 

mysql> select hid,t1.tname as hname ,mres,gid,t2.tnameas gname,matime

    -> from

    -> m left joint as t1

    -> on m.hid =t1.tid

    -> left join tas t2

    -> on m.gid =t2.tid;

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

| hid  | hname    | mres | gid  | gname   | matime     |

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

|    1 | 国安     | 2:0 |    2 | 申花     | 2006-05-21 |

|    2 | 申花     | 1:2 |    3 | 传智联队| 2006-06-21 |

|    3 | 传智联队| 2:5  |    1 | 国安     | 2006-06-25 |

|    2 | 申花     | 3:2 |    1 | 国安     | 2006-07-21 |

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

4 rows in set (0.00 sec)

 

6   union查询

6.1: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.

 

6.2:3期学员碰到的一道面试题

A表:

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

| id   | num  |

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

| a    |    5 |

| b    |   10 |

| c    |   15 |

| d    |   10 |

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

 

B表:

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

| id   | num  |

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

| b    |    5 |

| c    |   15 |

| d    |   20 |

| e    |   99 |

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

 

 

mysql> # 合并 ,注意all的作用

mysql> select * from ta

    -> union all

    -> select *from tb;

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

| id   | num  |

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

| a    |    5 |

| b    |   10 |

| c    |   15 |

| d    |   10 |

| b    |    5 |

| c    |   15 |

| d    |   20 |

| e    |   99 |

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

 

要求查询出以下效果:

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

| id   | sum(num) |

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

| a    |        5 |

| b    |       15 |

| c    |       30 |

| d    |       30 |

| e    |       99 |

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

 

参考答案:

mysql> # sum,group求和

mysql> select id,sum(num) from (select * from ta unionall select * from tb) as tmp group by id;

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

| id   | sum(num) |

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

| a    |        5 |

| b    |       15 |

| c    |       25 |

| d    |       30 |

| e    |       99 |

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

5 rows in set (0.00 sec)

 

 

7: 子查询:

7.1: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 wheregoods_id =(select max(goods_id) from ecs_goods);

 

 

7.2: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)

7.3: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 wheregoods_id in (select max(goods_id) from ecs_goods group by cat_id);

7.4: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 fromecs_goods order by goods_id desc) as t group by 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 whereid=new.gid

 

CREATE trigger tg3

after delete on ord

for each row

update goods set goods_number=good_number+old.num whereid=old.gid

 

 

CREATE  trigger tg4

after update on ord

for each row

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

 

2012-03-25更新,添加了面试案例

 

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