1.sql對大小寫不敏感
2.sql執行順序select--from--where--group by--having--order by 
3.SQL 使用單引號來環繞文字值（大部分資料庫系統也接受雙引號）。如果是數值，請不要使用引號。
4.ORDER BY 語句預設按照升序對記錄進行排序。


select name from persons
select * from persons
select name,sex from persons
select distinct name from persons

select * from persons where city='beijing
 
'
select * from persons where year>1996

select * from persons where firstname='thoma' and lastname='carter'
select * from persons where firstname='thoma' or lastname='carter'
select * from persons where (firstname='thoma' or firstname='willian') and lastname='carter'

select company,ordernumber from
 
 orders order by company
select company,ordernumber from orders order by company,ordernumber
select company,ordernumber from orders order by company desc
select company,ordernumber from orders order by company desc, ordernumber asc

insert into table_name values (1,2,3)
insert into table_name (name,sex,id) values
 
 ('yuanxu',1,2)

update persons set firstname='fred' where lastname='willian'
UPDATE Person SET Address = 'Zhongshan 23', City = 'Nanjing' WHERE LastName = 'Wilson'

delete from persons where name='bob'
delete from table_name
delete * from table_name

select * from persons limit 2
select top 2 * from persons
select top 50 percent * from persons

select * from persons where city like '%lon%'
select * from persons where city not like '%l'

select * from persons where lastname like 'C_r_er' 
我們希望從上面的 "Persons" 表中選取居住的城市以 "A" 或 "L" 或 "N" 開頭的人
select * from persons where city like '[ALN]%'
select * from persons where city like '[!ALN]%'
select * from persons where city like '[^ALN]%'

select * from persons where lastname in ('adams','carter')

select * from persons where lastname between 'adams' and 'carter'
select * from persons where lastname not between 'adams' and 'carter'

別名
SELECT po.OrderID, p.LastName, p.FirstName
FROM Persons AS p, Product_Orders AS po
WHERE p.LastName='Adams' AND p.FirstName='John'

SELECT LastName AS Family, FirstName AS Name
FROM Persons

SELECT Persons.LastName, Persons.FirstName, Orders.OrderNo
FROM Persons, Orders
WHERE Persons.Id_P = Orders.Id_P 

SELECT Persons.LastName, Persons.FirstName, Orders.OrderNo
FROM Persons
INNER JOIN Orders
ON Persons.Id_P = Orders.Id_P
ORDER BY Persons.LastName

UNION 操作符用於合併兩個或多個 SELECT 語句的結果集。
請注意，UNION 內部的 SELECT 語句必須擁有相同數量的列。列也必須擁有相似的資料型別。同時，每條 SELECT 語句中的列的順序必須相同。
SELECT E_Name FROM Employees_China
UNION
SELECT E_Name FROM Employees_USA

SELECT E_Name FROM Employees_China
UNION ALL
SELECT E_Name FROM Employees_USA

備份表
select * into persons_back from persons
select * into persons in 'backup.mdb' from persons
select lastname,firstname into persons_backup from persons
select lastname,firstname into persons_backup from persons where cirt='beijing'

SELECT Persons.LastName,Orders.OrderNo
INTO Persons_Order_Backup
FROM Persons
INNER JOIN Orders
ON Persons.Id_P=Orders.Id_P

create database my_db
create table persons {ip int, name varchar(255)}

create index personindex on person(lastname desc)
create index personindex on person (lastname, firstname)

CREATE VIEW [Current Product List] AS
SELECT ProductID,ProductName
FROM Products
WHERE Discontinued=No