//create database(創建數據庫)
create database my_db
//創建表
create table user( id int(11) not null auto_increment, name varchar(50) default null, password varchar(50) default null, primary key(id) )
//約束 not null (不爲null值) unique (唯一) primary key(主鍵) foreign key(外鍵) check(查詢約束) default(默認值約束)
//create index (創建索引)
create index ff on user (name,Address)
//distinct 關鍵字查詢字段的唯一值記錄，重複的字段值只會顯示一條查詢記錄
SELECT distinct name FROM user
//and(並且) or(或)查詢where語句的條件
SELECT * FROM user where City=”上海” and name=”admian3”
SELECT * FROM user where City=”上海” or name=”admian3”
//如果and 和or 結合來用的時候則要用到()處理
SELECT * FROM user where (City=”上海” or name = “admian3”) and name=”xxx”
//order by(關鍵字排序)(按照名字的順序來做升序排序)
select * from user order by name
//order by 後面可以接多個排序列表中間用,隔開
select * from user order by name,City,….
//desc (降序的關鍵字)
select * from user order by name desc
//asc (升序的關鍵字 order by 後面不跟有降序的關鍵字那麼就是默認爲升序)
select * from user order by name desc,City asc
//添加數據
insert into user(name,password,Address,City,OrderNumber)values(“ddsds”,”ssss”,”廣東”,”廣州”,1234656)
//更新數據
upate user set name=”ffff” where id =6 //刪除數據 delete from user where id = 6
//limit (關鍵字是查詢數據庫中多少條數據 再mysql裏面用，如果是sql server用則用top )
select * form user limit 2
//in (關鍵字允許我們在where語句中存在多個條件)
select * from user where name in(“xxxxs”,”zdasdsa”)
//between ….and..(關鍵字是處理在什麼之間到什麼之間的操作)
select * from user where name between “fffff” and “ssss”
//as(關鍵字是用於給表或數據庫起一個別名)
select * name as n,password as p from user
//inner join (關鍵字使用了內連接來查詢兩個表的數據,其中還有 left join(左連接) right join(右連接) full join(左右連接))
select u.name,u.Address,n.number from user as u “inner join” number as n on u.id = n.user_id order by u.Address
//union(命令將兩條sql語句拼接起來)
select * from user union select * from number
//select into(關鍵字是爲了把一個表的數據插入到另一個表當中)
select * into user from number