Mysql基礎+select5種子句

MySQL · 發表 2019-03-13 10:45:10

摘要： 1、建立練習的表 create table goods ( goods_id mediumint(8) unsigned primary key auto_increment, goods_name varchar(120) not null default '',...

1、建立練習的表

create table goods (
goods_id mediumint(8) unsigned primary key auto_increment,
goods_name varchar(120) not null default '',
cat_id smallint(5) unsigned not null default '0',
brand_id smallint(5) unsigned not null default '0',
goods_sn char(15) not null default '',
goods_number smallint(5) unsigned not null default '0',
shop_price decimal(10,2) unsigned not null default '0.00',
market_price decimal(10,2) unsigned not null default '0.00',
click_count int(10) unsigned not null default '0'
) engine=myisam default charset=utf8複製程式碼

插入資料

insert into `goods` values (1,'kd876',4,8,'ecs000000',1,1388.00,1665.60,9),
(4,'諾基亞n85原裝充電器',8,1,'ecs000004',17,58.00,69.60,0),
(3,'諾基亞原裝5800耳機',8,1,'ecs000002',24,68.00,81.60,3),
(5,'索愛原裝m2卡讀卡器',11,7,'ecs000005',8,20.00,24.00,3),
(6,'勝創kingmax記憶體卡',11,0,'ecs000006',15,42.00,50.40,0),
(7,'諾基亞n85原裝立體聲耳機hs-82',8,1,'ecs000007',20,100.00,120.00,0),
(8,'飛利浦9@9v',3,4,'ecs000008',1,399.00,478.79,10),
(9,'諾基亞e66',3,1,'ecs000009',4,2298.00,2757.60,20),
(10,'索愛c702c',3,7,'ecs000010',7,1328.00,1593.60,11),
(11,'索愛c702c',3,7,'ecs000011',1,1300.00,0.00,0),
(12,'摩托羅拉a810',3,2,'ecs000012',8,983.00,1179.60,13),
(13,'諾基亞5320 xpressmusic',3,1,'ecs000013',8,1311.00,1573.20,13),
(14,'諾基亞5800xm',4,1,'ecs000014',1,2625.00,3150.00,6),
(15,'摩托羅拉a810',3,2,'ecs000015',3,788.00,945.60,8),
(16,'恆基偉業g101',2,11,'ecs000016',0,823.33,988.00,3),
(17,'夏新n7',3,5,'ecs000017',1,2300.00,2760.00,2),
(18,'夏新t5',4,5,'ecs000018',1,2878.00,3453.60,0),
(19,'三星sgh-f258',3,6,'ecs000019',12,858.00,1029.60,7),
(20,'三星bc01',3,6,'ecs000020',12,280.00,336.00,14),
(21,'金立 a30',3,10,'ecs000021',40,2000.00,2400.00,4),
(22,'多普達touch hd',3,3,'ecs000022',1,5999.00,7198.80,16),
(23,'諾基亞n96',5,1,'ecs000023',8,3700.00,4440.00,17),
(24,'p806',3,9,'ecs000024',100,2000.00,2400.00,35),
(25,'小靈通/固話50元充值卡',13,0,'ecs000025',2,48.00,57.59,0),
(26,'小靈通/固話20元充值卡',13,0,'ecs000026',2,19.00,22.80,0),
(27,'聯通100元充值卡',15,0,'ecs000027',2,95.00,100.00,0),
(28,'聯通50元充值卡',15,0,'ecs000028',0,45.00,50.00,0),
(29,'移動100元充值卡',14,0,'ecs000029',0,90.00,0.00,0),
(30,'移動20元充值卡',14,0,'ecs000030',9,18.00,21.00,1),
(31,'摩托羅拉e8 ',3,2,'ecs000031',1,1337.00,1604.39,5),
(32,'諾基亞n85',3,1,'ecs000032',4,3010.00,3612.00,9);複製程式碼

查詢中用到的關鍵詞主要包含六個，並且他們的順序依次為
select--from--where--group by--having--order by複製程式碼

2、Where 條件查詢

①where expression

用法:expression為真,則該行取出

運用場合

各種條件查詢場合,如按學號查學生,按價格查商品,按釋出時間查新聞等

②select 5種子句之where常用運算子

③select 5種子句之where 匹配

like 模糊匹配 % 通配任意字元 _ 通配單一字元

2.1 取出goods表價格低於或等於100元的商品

select goods_id,cat_id,goods_name,shop_price from goods where shop_price <= 100;複製程式碼

2.2 取出第4欄目和第11欄目的商品(不許用or)

select goods_id,cat_id,goods_name,shop_pricefrom goods where cat_id in (4, 11);複製程式碼

2.3 取出100<=價格<=500的商品(不許用and)

select goods_id,cat_id,goods_name,shop_pricefrom goods where shop_price between 100 and 500;複製程式碼

2.3 取出名字以"諾基亞"開頭的商品

select goods_id,cat_id,goods_name,shop_pricefrom goods where goods_name like '諾基亞%';複製程式碼

2.4 取出名字為"諾基亞Nxx"的手機

select goods_id,cat_id,goods_name,shop_pricefrom goods where goods_name like '諾基亞n__';
複製程式碼

2.5 查出本店價格比市場價格省200元以上的商品

select goods_id, goods_name,abs(market_price-shop_price) as discount from goods
where (market_price-shop_price)>200;複製程式碼

3、group by 分組

①select 5種子句之group與統計函式

max : 求最大 min : 求最小 sum : 求總和 avg : 求平均 count:求總行數

②select 5種子句之group介紹

group by

作用:把行按欄位分組

語法:group by col1,col2,...colN

運用場合

常見於統計場合,如按欄目計算帖子數, 統計每個人的平均成績等.

3.1 group與統計函式

max: 求最大值
min: 求最小值
sum: 求總和
avg: 求平均
count: 求總行數（count不能識別null）

3.2 計算每一種商品的庫存數量之和

select goods_name,sum(goods_number) from goods group by goods_name;複製程式碼

4、having 篩選

①select 5種子句之having介紹

having 與where異同點

having 與where類似，可篩選資料

where後的表示式怎麼寫，having就怎麼寫

where針對表中的列發揮作用,查詢資料

having針對查詢結果中的列發揮作用,篩選資料

4.1 查詢每個欄目下，積壓的貨款，且篩選出積壓金額>20000的欄目

select cat_id,sum(goods_number*shop_price) as sumMoney from goods group by cat_id 
having sumMoney > 20000複製程式碼

4.2 where-having-group綜合練習題

# 建表
create table result (
name varchar(20),
subject varchar(20),
score tinyint
)engine myisam charset utf8;複製程式碼

# 插入資料
insert into result
values
('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)複製程式碼

# 查詢出2門及2門以上不及格者的平均成績
select name,sum(score < 60) as gk ,avg(score) as pj from result group by name having gk >=2;複製程式碼

5、order by 排序

①select 5種子句之order排序

Order by 排序功能

按一個或多個欄位對查詢結果進行排序

用法:order by col1,col2,col3

知識點的運用場合描述

各種排序場合,如新聞按點選量排序, 商品按價格排序等

預設排序:升續排列

5.1 按欄目升序排列，同一欄目下的商品，再按商品的價格降序排列

# asc代表升序，desc代表降序
select goods_id,cat_id,goods_name,shop_price
from goods
order by cat_id asc, shop_price desc複製程式碼

6、limit 限制結果條數

①select 5種子句之limit 介紹

Limit 限制條數

limit [offset,] N,限制結果取N條

用法: limit [偏移量,],取出條目