mysql 基础

建表例： create table t1( sn int, name varchar(18) );set names gbk; 转换编码 mysql复习一:复习前的准备1:确认你已安装wamp2: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主机查看表的结构:desc+表；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;表，视图管理语句查看表结构 desc 表名或视图名查看建表过程 show create table 表名查看建视图过程 show create view 视图名删除表 drop table 表名删除视图 drop view 视图名查看表详细信息 show table status查看某张表详细信息 show table stauts where name=‘表名’；改表名 rename table oldname to newname清空数据 truncate 表名  （相当于删掉表再重建）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;查看表的结构:desc+表；3.3 查看表的创建过程: show create table  tableName;3.4 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/gbk3.4的例子: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;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)alter table table1 add transactor varchar(10) not Null;alter table   table1 add id int unsigned not Null auto_increment primary key3.5.2修改表之修改列alter table tbNamechange 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)例：Alter table tt modify `tt_t` nvarchar3.5.3修改表之减少列:alter table tbName drop 列名称;alter table 表名 add 列名 列类型 列属性   默认值alter table 表名 add 列名 列类型 列属性  after 列名（）alter table 表名 drop column 列名alter table 表名change height 原列名 新列名alter table 表名 modify 新属性（增删改）3.5.4修改表之增加主键主键与自增主键 primary key 此列不重复，能够区分每一行例1： create table t6 (    -> id int primary key,    -> name char(2)); 例2：create table t7 (    -> id int,    -> name char(2),    -> primary key(id) );create table t7 (id int primary key auto_increment,               //自增型主键);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;索引操作查看 show index from 表名或 create table 表名也能看到删除 alter table 表明 drop index 索引名或 drop index 索引名 on 表名添加索引alter table 表名 add [index/unique] 索引名（列名）添加主键索引alter table 表名 add primary key（列名）；删除主键索引 drop primary key；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: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%                   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……); 例：insert into m(mid,hid) values(5,2);5.3修改数据update tablename set col1=newval1,  col2=newval2,......colN=newvalNwhere 条件;例： update m set mres='9:9',matime='1969-12-30' where mid=5;5.4，删除数据    delete from tablenaeme where 条件;例：delete from m where mid=7;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例： select matime from m  where mid=2;     select hid,matime from m where mid>=2;6:连接查询6.1， 左连接.. left join .. ontable 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.col22.  右链接: right join3.  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 tgNameafter/before insert/delete/update on tableNamefor each rowsql; -- 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:goodsgoods_id　--主键,goods_name -- 商品名称cat_id  -- 栏目idbrand_id -- 品牌idgoods_sn -- 货号goods_number -- 库存量shop_price  -- 价格goods_desc　--商品详细描述栏目表:categorycat_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5320 XpressMusic       |      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Touch HD               |      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.:主键为32的商品select goods_id,goods_name,shop_price      from ecs_goods     where goods_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 select goods_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_price between 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 and shop_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_count from ecs_goods wherecat_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_count from 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_name like '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_name not 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 and click_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%';1.15 一道面试题有如下表和数组把num值处于[20,29]之间,改为20num值处于[30,39]之间的,改为30例： update m set mres='9:9',matime='1969-12-30' where mid=5;mian表+------+| num  |+------+|    3 ||   12 ||   15 ||   25 ||   23 ||   29 ||   34 ||   37 ||   32 ||   45 ||   48 ||   52 |+------+update mian set num=floor(num/10)*10 where num >=20 and num <=39;1.16 练习题:把goods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()select goods_id,concat('HTC',substring(goods_name,4)) from goods where goods_name like '诺基亚%';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 select avg(shop_price) from ecs_goods;2.7:查询该店一共有多少种商品 select count(*) from ecs_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_goods3.3: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 from ecs_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_goodswhere market_price-shop_price >200;select goods_id,goods_name,market_price-shop_price  as k from ecs_goodshaving 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 from ecs_goods group by cat_idhaving k>200003.7: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4.1:按价格由高到低排序select goods_id,goods_name,shop_price from ecs_goods order by shop_price desc;4.2: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;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 order by 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 order by 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_categoryon 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_categoryon ecs_goods.cat_id=ecs_category.cat_idwhere 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_categoryon ecs_goods.cat_id=ecs_category.cat_idleft join ecs_brand on ecs_goods.brand_id=ecs_brand.brand_idwhere 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matchIDint主键hostTeamIDint主队的IDguestTeamIDint客队的IDmatchResultvarchar(20)比赛结果，如（2:0）matchTimedate比赛开始时间Team 参赛队伍表字段名称字段类型描述teamIDint主键teamNamevarchar(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 2006-6-21mysql> 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 | 公益联队 |+------+----------+3 rows in set (0.00 sec)mysql> select hid,t1.tname as hname ,mres,gid,t2.tname as gname,matime    -> from     -> m left join t as t1    -> on m.hid = t1.tid    -> left join t as 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 | 公益联队 | 2006-06-21 ||    3 | 公益联队 | 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)6union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 |+------+------+要求查询出以下效果:+------+----------+| id   |    num   |+------+----------+| a    |        5 || b    |       15 || c    |       30 || d    |       30 || e    |       99 |+------+----------+create table a (id char(1),num int)engine myisam charset utf8;insert into a values ('a',5),('b',10),('c',15),('d',10);create table b (id char(1),num int)engine myisam charset utf8;insert into b values ('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 |+------+------+参考答案:mysql> # sum,group求和mysql> select id,sum(num) from (select * from ta union all select * from tb) as tmp group by id; +------+----------+| id   | sum(num) |+------+----------+| a    |        5 || b    |       15 || c    |       30 || 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 where goods_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 where goods_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 from ecs_goods order by goods_id desc) as t group by cat_id;7.5 用exists型子查询,查出所有有商品的栏目select * from categorywhere exists (select * from goods where goods.cat_id=category.cat_id);创建触发器: CREATE  trigger tg2after insert on ordfor each rowupdate goods set goods_number=goods_number-new.num where id=new.gidCREATE trigger tg3after delete on ordfor each rowupdate goods set goods_number=good_number+old.num where id=old.gidCREATE  trigger tg4after update on ordfor each rowupdate goods set goods_number=goods_number+old.num-new.num where id=old.gid

2012-03-25更新,添加了面试案例