1) Order by
1.order by子句应在select语句的最后一条子句
2.select prod_id, prod_price, prod_name from Products order by prod_price, prod_name
仅在多行具有相同的prod_price时才对产品按prod_name排序。
相当于select prod_id, prod_price, prod_name from Products order by 2, 3
3.order by默认为升序排列，降序排列为DESC
select prod_id, prod_price, prod_name from Products order by prod_price DESC, prod_name
2) IN 和 OR
1.IN和OR效果相同
select prod_price, prod_name from Products where prod_id='ID01' OR prod_id=‘ID02’ and prod_price >= 10
相当于
select prod_price, prod_name from Products where prod_id IN('ID01','ID02') and prod_price >= 10
AND和OR同时存在时，优先处理and操作符。
2.IN操作符一般比OR操作符更快
3.select cust_id from orders where order_num IN(select order_num from OrderItems where prod_id = 'RGAN01')
3) NOT和<>
select prod_price, prod_name from Products where NOT prod_id = 'ID01'
等价于
select prod_price, prod_name from Products where prod_id<>'ID01'
(MYSQL中NOT只用来否定EXISTS)
4) 通配符
select prod_price, prod_name from Products where prod_name LIKE 'Fish%' 匹配多个字符
select prod_price, prod_name from Products where prod_name LIKE '_ish' 匹配单个字符
select prod_price, prod_name from Products where prod_name LIKE '[JM]%' 查找J或M开头的名字
select prod_price, prod_name from Products where prod_name LIKE '[^JM]%' 查找不以J或M开头的名字
5) TRIM, RTRIM, LTRIM 去空格
select vend_name+'('+vend_country+')' from vendors order by vend_name
其结果为：HUAWEI (CHINA )
因为许多数据库保存填充为列宽的文本值。
select RTRIM(vend_name)+'('+RTRIM(vend_country)+')' from vendors order by vend_name
其结果为：HUAWEI(CHINA)
RTRIM去右边空格，LTRIM去左边空格，TRIM去两边空格
（
MYSQL不支持+或||的拼接，而用CONCAT()
select CONCAT(vend_name,'('，vend_country,')');
）
6)计算字段
select prod_id,quantity,item_price,quantity*item_price AS expanded_price from OrderItems where order_num = 200
select AVG(prod_price) AS avg_price from Products
select AVG(DISTINCT prod_price) AS avg_price from Products 使用了DISTINCT平均值只考虑各个不同的价格
select COUNT(*) AS num_count from Customers 对表中行数进行计算
select COUNT(cust_email) AS num_count from Customers 对表中特定列，不为空的行数进行计算
select MAX(prod_price) AS max_price from Products
select SUM(quantity*item_price) AS total_price from Orders where order_num = 200
7)提取字串
SQL SERVER: SUBSTRING()
8)数据类型转换
SQL SERVER、MYSQL： CONVERT()
9)取当前日期
SQL SERVER:GETDATE()
MYSQL :CURDATE()
10)大小写转换
select UPPER(vend_name) as vend_name_upcase from Vendors order by vend_name
11)group by
select shop_id, SUM(shop_income) from Shops where Date > 20141101 and Date <20141115 group by shop_id
按店铺编号查找某日期段内的收入
12)having
select cust_id,cout(*) AS order from Orders GROUP BY cust_id HAVING count(*) >=2
having用来过滤分组；where在数据分组前过滤，having在分组后过滤
select order_num, count(*) AS items from OrderItems GROUP BY order_num HAVING count(*)>=3 ORDER BY items, order_num
13)INNER JOIN
select vend_name,prod_name,prod_price from Vendors INNER JOIN Products ON Vendors.vend_id = Products.vend_id
select vend_name,prod_name,prod_price from Vendors,Products where Vendors.vend_id = Products.vend_id
两者等价
14)UNION
select cust_name, cust_contact, cust_email from Customers where cust_state IN('IL','IN','MI')
UNION
select cust_name, cust_contact, cust_email from Customers where cust_name = 'Fun4All'
UNION从查询结果中去除了重复的行，要返回所有行，可用UNION ALL
15)复制表insert into select和 select into
insert into Customers(cust_id,cust_name,cust_email) select cust_id,cust_name,cust_email from CustNew;
从CustNew中将所有数据导入Customers
INSERT SELECT 使用的是列的位置，将select的第一列填充表列中指定的第一列，用第二列填充第二列，而不关心select返回的列名
insert select是增补数据到一个已存在的表，而select into 是复制数据到一个新表
insert select是导出数据，select into是导入表
select * into Cust from Customers
16)创建表Create
create table Products
(
prod_id CHAR(10) NOT NULL PRIMARY KEY，
vend_id CHAR(10) NOT NULL ,
prod_price DECIMAL(8,2) NOT NULL,
quantity INTEGER NOT NULL DEFAULT 1 CHECK(quantity > 0) //指定默认值 , 设置约束条件
)
17)修改表
update Customers set cust_name='a',cust_email = '88.com' where cust_id = '1006'
delete from Customers where cust_id = '1006'
alter table Vendors add vend_phone CHAR(20)
alter table Vendors add CONSTRAINT PRIMARY KEY(vend_id)
alter table Vendors drop Column vend_phone
18)创建视图
CREATE VIEW ProductCustomers AS
SELECT cust_name, cust_contacr, prod_id
FROM Customers, Orders, OrderItems
WHERE Customers.cust_id = Orders.cust_id
AND OrderItems.order.num = Orders.order_num;
查询视图：
select cust_name, cust_contact from ProductCustomers where prod_id = '1003'
三个条件会自动组合
19)存储过程
在Orders表中增加一个新订单
CREATE PROCEDURE NewOrder @cust_id CHAR(10) AS
DECLARE @order_num INTEGER
SELECT @order_num = MAX(order_num)
FROM Orders
SELECT @order_num = @order_num + 1
INSERT INTO Orders(order_num, order_date, cust_id)
VALUES(@order_num, GETDATE(), @cust_id)
RETURN @order_num
EXCUTE NewOrder cust_id号(下单客户的ID)
20)事务处理
BEGIN TRANSACTION
INSERT INTO Customers(cust_id,cust_name)
VALUES('1001','Toys');
SAVE TRANSACTION StartOrder;
INSERT INTO Orders(order_num, order_date, cust_id)
VALUES(20100,'2001/12/01','1001');
IF @@ERROR <>0 ROLLBACK TRANSACTION StartOrder;
INSERT INTO OrderItems(cust_num, order_item, prod_id, quantity, item_price)
VALUES(20100,1,'BR01', 100, 5.24);
IF @@ERROR <> 0 ROLLBACK TRANSACTION StartOrder;
COMMIT TRANSACTION