萬盛學電腦網 >> 數據庫 >> mysql教程 >> mysql數據庫入門教程之學習筆記
mysql數據庫入門教程之學習筆記
mysql復習
一:復習前的准備
1:確認你已安裝wamp
2:確認你已安裝ecshop,並且ecshop的數據庫名為shop
二 基礎知識:
1.數據庫的連接
mysql -u -p -h
-u 用戶名
-p 密碼
-h host主機
2:庫級知識
2.1 顯示數據庫: show databases;
2.2 選擇數據庫: use dbname;
2.3 創建數據庫: create database dbname charset utf8;
2.3 刪除數據庫: drop database dbname;
3: 表級操作:
3.1 顯示庫下面的表
show tables;
3.2 查看表的結構:
desc tableName;
3.3 查看表的創建過程:
show create table tableName;
3.4 創建表:
create table tbName (
列名稱1 列類型 [列參數] [not null default ],
....列2...
....
列名稱N 列類型 [列參數] [not null default ]
)engine myisam/innodb charset utf8/gbk
3.4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 列名稱１ 列類型 [列參數] [not null default ] #(add之後的舊列名之後的語法和創建表時的列聲明一樣)
3.5.2 修改表之修改列
alter table tbName
change 舊列名 新列名 列類型 [列參數] [not null default ]
(注:舊列名之後的語法和創建表時的列聲明一樣)
3.5.3 修改表之減少列:
alter table tbName
drop 列名稱;
3.5.4 修改表之增加主鍵
alter table tbName add primary key(主鍵所在列名);
例:alter table goods add primary key(id)
該例是把主鍵建立在id列上
3.5.5 修改表之刪除主鍵
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 修改表之刪除索引
alter table tbName drop index 索引名;
3.5.8 清空表的數據
truncate tableName;
4:列類型講解
列類型:
整型:tinyint (0~255/-128~127) smallint (0~65535/-32768~32767) mediumint int bigint (參考手冊11.2)
參數解釋:
unsigned 無符號(不能為負) zerofill 0填充 M 填充後的寬度
舉例:tinyint unsigned;
tinyint(6) zerofill;
數值型
浮點型:float double
格式:float(M,D) unsignedzerofill;
字符型
char(m) 定長
varchar(m)變長
text
列 實存字符i 實占空間 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 范圍:1901~2155. 可輸入值2位和4位(如98,2012)
日期時間類型 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:不用賦值,該列會為自己賦當前的具體時間
5:增刪改查基本操作
5.1 插入數據
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修改數據
update tablename
set
col1=newval1,
col2=newval2,
...
...
colN=newvalN
where 條件;
5.4，刪除數據 delete from tablenaeme where 條件;
5.5， select 查詢
（1） 條件查詢 where a. 條件表達式的意義，表達式為真，則該行取出
b. 比較運算符 = ，!=，< > <= >=
c. like , not like ("%"匹配任意多個字符,"_"匹配任意單個字符)
in , not in , between and
d. is null , is not null
（2） 分組 group by
一般要配合5個聚合函數使用:max,min,sum,avg,count
（3） 篩選 having
（4） 排序 order by
（5） 限制 limit
6: 連接查詢
6.1， 左連接
.. 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. 右鏈接: right join
3. 內連接: inner join
左右連接都是以在左邊的表的數據為准,沿著左表查右表.
內連接是以兩張表都有的共同部分數據為准,也就是左右連接的數據之交集.
7 子查詢
where 型子查詢:內層sql的返回值在where後作為條件表達式的一部分
例句: select * from tableA where colA = (select colB from tableB where ...);
from 型子查詢:內層sql查詢結果,作為一張表,供外層的sql語句再次查詢
例句:select * from (select * from ...) as tableName where ....
8: 字符集
客服端sql編碼 character_set_client
服務器轉化後的sql編碼 character_set_connection
服務器返回給客戶端的結果集編碼 character_set_results
快速把以上3個變量設為相同值: set names 字符集
存儲引擎 engine=12
1 Myisam 速度快 不支持事務 回滾
2 Innodb 速度慢 支持事務,回滾
①開啟事務 start transaction
②運行sql;
③提交,同時生效回滾 commit
ollback
觸發器 trigger
監視地點:表
監視行為:增 刪 改
觸發時間:afterefore
觸發事件:增 刪 改
創建觸發器語法
create trigger tgName
after/before insert/delete/update
on tableName
for each row
sql; -- 觸發語句
刪除觸發器:drop trigger tgName;
索引
提高查詢速度,但是降低了增刪改的速度,所以使用索引時,要綜合考慮.
索引不是越多越好,一般我們在常出現於條件表達式中的列加索引.
值越分散的列，索引的效果越好
索引類型
primary key主鍵索引
index 普通索引
unique index 唯一性索引
fulltext index 全文索引
綜合練習:
連接上數據庫服務器
創建一個gbk編碼的數據庫
建立商品表和欄目表,字段如下:
商品表:goods
goods_id --主鍵,
goods_name -- 商品名稱
cat_id -- 欄目id
brand_id -- 品牌id
goods_sn -- 貨號
goods_number -- 庫存量
shop_price -- 價格
goods_desc --商品詳細描述
欄目表:category
cat_id --主鍵
cat_name -- 欄目名稱
parent_id -- 欄目的父id
建表完成後,作以下操作:
刪除goods表的goods_desc 字段,及貨號字段
並增加字段:click_count -- 點擊量
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
刪除click_count列上的索引
對goods表插入以下數據:
+----------+------------------------------+--------+----------+-----------+--------------+------------+-------------+
| 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 | 諾基亞N85原裝充電器 | 8 | 1 | ECS000004 | 17 | 58.00 | 0 |
| 3 | 諾基亞原裝5800耳機 | 8 | 1 | ECS000002 | 24 | 68.00 | 3 |
| 5 | 索愛原裝M2卡讀卡器 | 11 | 7 | ECS000005 | 8 | 20.00 | 3 |
| 6 | 勝創KINGMAX內存卡 | 11 | 0 | ECS000006 | 15 | 42.00 | 0 |
| 7 | 諾基亞N85原裝立體聲耳機HS-82 | 8 | 1 | ECS000007 | 20 | 100.00 | 0 |
| 8 | 飛利浦9@9v | 3 | 4 | ECS000008 | 17 | 399.00 | 9 |
| 9 | 諾基亞E66 | 3 | 1 | ECS000009 | 13 | 2298.00 | 20 |
| 10 | 索愛C702c | 3 | 7 | ECS000010 | 7 | 1328.00 | 11 |
| 11 | 索愛C702c | 3 | 7 | ECS000011 | 1 | 1300.00 | 0 |
| 12 | 摩托羅拉A810 | 3 | 2 | ECS000012 | 8 | 983.00 | 14 |
| 13 | 諾基亞5320 XpressMusic | 3 | 1 | ECS000013 | 8 | 1311.00 | 13 |
| 14 | 諾基亞5800XM | 4 | 1 | ECS000014 | 4 | 2625.00 | 6 |
| 15 | 摩托羅拉A810 | 3 | 2 | ECS000015 | 3 | 788.00 | 8 |
| 16 | 恆基偉業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 | 多普達Touch HD | 3 | 3 | ECS000022 | 0 | 5999.00 | 15 |
| 23 | 諾基亞N96 | 5 | 1 | ECS000023 | 8 | 3700.00 | 17 |
| 24 | P806 | 3 | 9 | ECS000024 | 148 | 2000.00 | 36 |
| 25 | 小靈通/固話50元充值卡 | 13 | 0 | ECS000025 | 2 | 48.00 | 0 |
| 26 | 小靈通/固話20元充值卡 | 13 | 0 | ECS000026 | 2 | 19.00 | 0 |
| 27 | 聯通100元充值卡 | 15 | 0 | ECS000027 | 2 | 95.00 | 0 |
| 28 | 聯通50元充值卡 | 15 | 0 | ECS000028 | 0 | 45.00 | 0 |
| 29 | 移動100元充值卡 | 14 | 0 | ECS000029 | 0 | 90.00 | 0 |
| 30 | 移動20元充值卡 | 14 | 0 | ECS000030 | 9 | 18.00 | 1 |
| 31 | 摩托羅拉E8 | 3 | 2 | ECS000031 | 1 | 1337.00 | 5 |
| 32 | 諾基亞N85 | 3 | 1 | ECS000032 | 1 | 3010.00 | 9 |
+----------+------------------------------+--------+----------+-----------+--------------+------------+-------------+
三 查詢知識
注:以下查詢基於ecshop網站的商品表(ecs_goods)
在練習時可以只取部分列,方便查看.
1: 基礎查詢 where的練習:
查出滿足以下條件的商品
1.1:主鍵為32的商品
select goods_id,goods_name,shop_price
from ecs_goods
where goods_id=32;
1.2:不屬第3欄目的所有商品
select goods_id,cat_id,goods_name,shop_price from ecs_goods
where cat_id!=3;
1.3:本店價格高於3000元的商品
select goods_id,cat_id,goods_name,shop_price from ecs_goods
where shop_price >3000;
1.4:本店價格低於或等於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欄目或第11欄目的商品(不許用or)
select goods_id,cat_id,goods_name,shop_price from ecs_goods
where cat_id in (4,11);
1.6:取出100<=價格<=500的商品(不許用and)
select goods_id,cat_id,goods_name,shop_price from ecs_goods
where shop_price between 100 and 500;
1.7:取出不屬於第3欄目且不屬於第11欄目的商品(and,或not in分別實現)
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:取出價格大於100且小於300,或者大於4000且小於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個欄目下面價格<1000或>3000,並且點擊量>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;
1.10:取出第1個欄目下面的商品(注意:1欄目下面沒商品,但其子欄目下有)
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"諾基亞"開頭的商品
select goods_id,cat_id,goods_name,shop_price from ecs_goods where goods_name like "諾基亞%";
1.12:取出名字為"諾基亞Nxx"的手機
select goods_id,cat_id,goods_name,shop_price from ecs_goods
where goods_name like "諾基亞N__";
1.13:取出名字不以"諾基亞"開頭的商品
select goods_id,cat_id,goods_name,shop_price from ecs_goos
where goods_name not like "諾基亞%";
1.14:取出第3個欄目下面價格在1000到3000之間,並且點擊量>5 "諾基亞"開頭的系列商品
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 "諾基亞%";
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 "諾基亞%";
一道面試題
有如下表和數組
把num值處於[20,29]之間,改為20
num值處於[30,39]之間的,改為30
mian表
+------+
| num |
+------+
| 3 |
| 12 |
| 15 |
| 25 |
| 23 |
| 29 |
| 34 |
| 37 |
| 32 |
| 45 |
| 48 |
| 52 |
+------+
練習題:
把good表中商品名為"諾基亞xxxx"的商品,改為"HTCxxxx",
提示:大膽的把列看成變量,參與運算,甚至調用函數來處理 .
substring(),concat()
2 分組查詢group:
2.1:查出最貴的商品的價格
select max(shop_price) from ecs_goods;
2.2:查出最大(最新)的商品編號
select max(goods_id) from ecs_goods;
2.3:查出最便宜的商品的價格
select min(shop_price) from ecs_goods;
2.4:查出最舊(最小)的商品編號
select min(goods_id) from ecs_goods;
2.5:查詢該店所有商品的庫存總量
select sum(goods_number) from ecs_goods;
2.6:查詢所有商品的平均價
select avg(shop_price) from ecs_goods;
2.7:查詢該店一共有多少種商品
select count(*) from ecs_goods;
2.8:查詢每個欄目下面
最貴商品價格
最低商品價格
商品平均價格
商品庫存量
商品種類
提示:(5個聚合函數,sum,avg,max,min,count與group綜合運用)
select cat_id,max(shop_price) from ecs_goods group by cat_id;
3 having與group綜合運用查詢:
3.1:查詢該店的商品比市場價所節省的價格
select goods_id,goods_name,market_price-shop_price as j
from ecs_goods ;
3.2:查詢每個商品所積壓的貨款(提示:庫存*單價)
select goods_id,goods_name,goods_number*shop_price from ecs_goods
3.3:查詢該店積壓的總貨款
select sum(goods_number*shop_price) from ecs_goods;
3.4:查詢該店每個欄目下面積壓的貨款.
select cat_id,sum(goods_number*shop_price) as k from ecs_goods group by cat_id;
3.5:查詢比市場價省錢200元以上的商品及該商品所省的錢(where和having分別實現)
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:查詢積壓貨款超過2W元的欄目,以及該欄目積壓的貨款
select cat_id,sum(goods_number*shop_price) as k from ecs_goods group by cat_id
having k>20000
3.7:where-having-group綜合練習題
有如下表及數據
+------+---------+-------+
| name | subject | score |
+------+---------+-------+
| 張三 | 數學 | 90 |
| 張三 | 語文 | 50 |
| 張三 | 地理 | 40 |
| 李四 | 語文 | 55 |
| 李四 | 政治 | 45 |
| 王五 | 政治 | 30 |
+------+---------+-------+
要求:查詢出2門及2門以上不及格者的平均成績
## 一種錯誤做法
mysql> select name,count(score<60) as k,avg(score) from stu group by name having k>=2;
+------+---+------------+
| name | k | avg(score) |
+------+---+------------+
| 張三 | 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) |
+------+---+------------+
| 張三 | 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) |
+------+---+------------+
| 張三 | 3 | 60.0000 |
| 李四 | 2 | 50.0000 |
+------+---+------------+
2 rows in set (0.00 sec)
#加上趙六後錯誤暴露
mysql> insert into stu
-> values
-> ("趙六","A",100),
-> ("趙六","B",99),
-> ("趙六","C",98);
Query OK, 3 rows affected (0.05 sec)
Records: 3 Duplicates: 0 Warnings: 0
#錯誤顯現
mysql> select name,count(score<60) as k,avg(score) from stu group by name having k>=2;
+------+---+------------+
| name | k | avg(score) |
+------+---+------------+
| 張三 | 3 | 60.0000 |
| 李四 | 2 | 50.0000 |
| 趙六 | 3 | 99.0000 |
+------+---+------------+
3 rows in set (0.00 sec)
#正確思路,先查看每個人的平均成績
mysql> select name,avg(score) from stu group by name;
+------+------------+
| name | avg(score) |
+------+------------+
| 張三 | 60.0000 |
| 李四 | 50.0000 |
| 王五 | 30.0000 |
| 趙六 | 99.0000 |
+------+------------+
4 rows in set (0.00 sec)
mysql> # 看每個人掛科情況
mysql> select name,score < 60 from stu;
+------+------------+
| name | score < 60 |
+------+------------+
| 張三 | 0 |
| 張三 | 1 |
| 張三 | 1 |
| 李四 | 1 |
| 李四 | 1 |
| 王五 | 1 |
| 趙六 | 0 |
| 趙六 | 0 |
| 趙六 | 0 |
+------+------------+
9 rows in set (0.00 sec)
mysql> #計算每個人的掛科科目
mysql> select name,sum(score < 60) from stu group by name;
+------+-----------------+
| name | sum(score < 60) |
+------+-----------------+
| 張三 | 2 |
| 李四 | 2 |
| 王五 | 1 |
| 趙六 | 0 |
+------+-----------------+
4 rows in set (0.00 sec)
#同時計算每人的平均分
mysql> select name,sum(score < 60),avg(score) as pj from stu group by name;
+------+-----------------+---------+
| name | sum(score < 60) | pj |
+------+-----------------+---------+
| 張三 | 2 | 60.0000 |
| 李四 | 2 | 50.0000 |
| 王五 | 1 | 30.0000 |
| 趙六 | 0 | 99.0000 |
+------+-----------------+---------+
4 rows in set (0.00 sec)
#利用having篩選掛科2門以上的.
mysql> select name,sum(score < 60) as gk ,avg(score) as pj from stu group by name having gk >=2;
+------+------+---------+
| name | gk | pj |
+------+------+---------+
| 張三 | 2 | 60.0000 |
| 李四 | 2 | 50.0000 |
+------+------+---------+
2 rows in set (0.00 sec)
4: order by 與 limit查詢
4.1:按價格由高到低排序
select goods_id,goods_name,shop_price from ecs_goods order by shop_price desc;
4.2:按發布時間由早到晚排序
select goods_id,goods_name,add_time from ecs_goods order by add_time;
4.3:接欄目由低到高排序,欄目內部按價格由高到低排序
select goods_id,cat_id,goods_name,shop_price from ecs_goods
order by cat_id ,shop_price desc;
4.4:取出價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:取出點擊量前三名到前5名的商品
select goods_id,goods_name,click_count from ecs_goods order by click_count desc limit 2,3;
5 連接查詢
5.1:取出所有商品的商品名,欄目名,價格
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個欄目下的商品的商品名,欄目名,價格
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個欄目下的商品的商品名,欄目名,與品牌名
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: 用友面試題
根據給出的表結構按要求寫出SQL語句。
Match 賽程表
字段名稱 字段類型 描述
matchID int 主鍵
hostTeamID int 主隊的ID
guestTeamID int 客隊的ID
matchResult varchar(20) 比賽結果，如（2:0）
matchTime date 比賽開始時間
Team 參賽隊伍表
字段名稱 字段類型 描述
teamID int 主鍵
teamName varchar(20) 隊伍名稱
Match的hostTeamID與guestTeamID都與Team中的teamID關聯
查出 2006-6-1 到2006-7-1之間舉行的所有比賽，並且用以下形式列出：
拜仁 2：0 不來梅 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 | 國安 |
| 2 | 申花 |
| 3 | 傳智聯隊 |
+------+----------+
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 | 國安 | 2:0 | 2 | 申花 | 2006-05-21 |
| 2 | 申花 | 1:2 | 3 | 傳智聯隊 | 2006-06-21 |
| 3 | 傳智聯隊 | 2:5 | 1 | 國安 | 2006-06-25 |
| 2 | 申花 | 3:2 | 1 | 國安 | 2006-07-21 |
+------+----------+------+------+----------+------------+
4 rows in set (0.00 sec)
6 union查詢
6.1:把ecs_comment,ecs_feedback兩個表中的數據,各取出4列,並把結果集union成一個結果集.
6.2:3期學員碰到的一道面試題
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> # 合並 ,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 |
+------+------+
要求查詢出以下效果:
+------+----------+
| id | sum(num) |
+------+----------+
| a | 5 |
| b | 15 |
| c | 30 |
| d | 30 |
| e | 99 |
+------+----------+
參考答案:
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 | 25 |
| d | 30 |
| e | 99 |
+------+----------+
5 rows in set (0.00 sec)
7: 子查詢:
7.1:查詢出最新一行商品(以商品編號最大為最新,用子查詢實現)
select goods_id,goods_name from
ecs_goods where goods_id =(select max(goods_id) from ecs_goods);
7.2:查詢出編號為19的商品的欄目名稱(用左連接查詢和子查詢分別)
7.3:用where型子查詢把ecs_goods表中的每個欄目下面最新的商品取出來
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型子查詢把ecs_goods表中的每個欄目下面最新的商品取出來
select * from (select goods_id,cat_id,goods_name from ecs_goods order by goods_id desc) as t group by cat_id;
創建觸發器:
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
