SQL基本练习

Posted 2021-01-19 yuanninesuns

1.sql对大小写不敏感
2.sql执行顺序select--from--where--group by--having--order by 
3.SQL 使用单引号来环绕文本值（大部分数据库系统也接受双引号）。如果是数值，请不要使用引号。
4.ORDER BY 语句默认按照升序对记录进行排序。


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‘ 
我们希望从上面的 "Persons" 表中选取居住的城市以 "A" 或 "L" 或 "N" 开头的人
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‘

别名
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 操作符用于合并两个或多个 SELECT 语句的结果集。
请注意，UNION 内部的 SELECT 语句必须拥有相同数量的列。列也必须拥有相似的数据类型。同时，每条 SELECT 语句中的列的顺序必须相同。
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

备份表
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