SQL必知必会学习笔记--20180626

刚看完《SQL必知必会》的PDF文档，总结一下学习过程中记录下来的笔记。这本书讲的是SQL的基础知识，内容非常粗浅，比较适合初学者。
第一章的数据库基础，没有代码，基本就是一些关于列，表，主键的定义，已掌握，忽略。从第二章开始总结。

SELECT检索

---检索单个列
select CustomerNo from Customers;

通配符的使用

select *from dbo.Customers;
select CustomerNo from dbo.Customers
where CustomerNo LIKE'[AQ]%';--[]表示中括号中内容任取其一，%指代任意多个字符
SELECT CustomerNo FROM Customers
WHERE CustomerNo LIKE '_TM00_';--_指代任意单个字符

拼接字段

select CustomerNo+'('+CustomerState+')' 
AS CustomerTitle
from dbo.Customers
ORDER BY CustomerNo DESC;--将两列合并成一列并取别名为CustomerTitle，按照CustomerNo降序排列

文本处理函数的使用RTRIM和LTRIM

SELECT RTRIM(CustomerNo)+'('+RTRIM(CustomerState)+')'
AS CustomerTitle
FROM Customers
ORDER BY CustomerNo DESC;--在上一条语句的基础上去掉字符串右边的空格

ORDER BY排序并以列号指代某一列

SELECT CustomerNo,CustomerShortName,CustomerState,Class from dbo.Customers
ORDER BY 4 DESC,2;

NOT操作符，检索除某一项之外的所有数据

SELECT CustomerNo FROM dbo.Customers
WHERE NOT CustomerNo LIKE'[QC]%'

IN操作符，检索在某个条件范围内的数据

SELECT CustomerNo,Class FROM dbo.Customers
WHERE CustomerNo IN ('ATM002','QTM104','ATM004')
ORDER BY 2 DESC;

文本处理函数UPPER和LOWER的使用，将列值转换为大写或者转换成小写

SELECT UPPER(CustomerNo) AS CUS,Class FROM dbo.Customers
WHERE CustomerNo LIKE 'Cus%';

SELECT LOWER(CustomerNo) AS cus,Class FROM dbo.Customers
WHERE CustomerNo LIKE '_TM%'

时间处理函数DATEPART的使用，取时间值中的某一项数据

SELECT Created from dbo.Inspections
WHERE DATEPART(YY,Created)=2018;

聚集函数AVG,COUNT,MAX,MIN,SUM的使用

SELECT AVG(TotalAmount) AS AvgAmount FROM dbo.Inspections;--平均值函数

SELECT COUNT(*) AS CountNum FROM dbo.Customers--计数函数
WHERE CustomerState='销售机会';
SELECT CustomerNo FROM dbo.Customers
WHERE CustomerState='销售机会';

SELECT MAX(TotalAmount) AS MaxAmount FROM dbo.Inspections;--最大值函数
SELECT * FROM dbo.Inspections WHERE TotalAmount='126000'

SELECT * FROM dbo.Inspections;
SELECT SUM(TotalVolumn) AS SumV FROM dbo.Inspections;--求和函数
SELECT TotalAmount+TotalGrossWeight AS SumV FROM dbo.Inspections;

SELECT COUNT(*) AS countNo,
MIN(TotalVolumn) AS minTV,
MAX(TotalVolumn) AS maxTV,
AVG(TotalVolumn) AS avgTV
FROM dbo.Inspections

分组函数GROUP BY

SELECT COUNT(*) AS countNO
FROM dbo.Customers
WHERE CustomerNo LIKE '_TM%'
GROUP BY CustomerState;

对组处理条件函数HAVING,对已分组的组进行进一步筛选

SELECT CustomerState,COUNT(*) AS countNo
FROM dbo.Customers
WHERE CustomerNo LIKE '_TM%'
GROUP BY CustomerState
HAVING CustomerState='产品认可';

内联结，联结多个表的查询语句

SELECT * FROM dbo.Quotations;
SELECT QuotationNo,QuotationStatus,Class From Quotations,Customers
WHERE Quotations.CustomerNo=Customers.CustomerNo;

SELECT QuotationNo,QuotationStatus,Class FROM Quotations INNER JOIN Customers
ON Quotations.CustomerNo=Customers.CustomerNo;

将多表联结转化为子查询语句

SELECT QuotationNo,QuotationStatus FROM Quotations,Customers
where Customers.CustomerState='销售机会'
AND Customers.CustomerNo=Quotations.CustomerNo;

SELECT QuotationNo,QuotationStatus FROM Quotations
WHERE Quotations.CustomerNo IN(
    SELECT CustomerNo FROM Customers
    WHERE Customers.CustomerState='销售机会');--要求查询结果的所有列都在同一张表中才能与多表联结互相转化

表别名

SELECT Q.QuotationNo,Q.QuotationStatus,C.Class FROM Quotations Q,Customers C
WHERE C.CustomerState='销售机会'
AND Q.CustomerNo=C.CustomerNo;

SELECT QuotationNo,QuotationStatus,Class
FROM Quotations Q,Customers C
WHERE Q.QuotationStatus='处理中'
AND Q.CustomerNo=C.CustomerNo
AND C.CustomerState='销售机会';

自联结

SELECT C1.CustomerNo,C1.Class,C1.CustomerState
FROM Customers C1,Customers C2
WHERE C2.CustomerNo='CTM002'
AND C1.Class=C2.Class;--列出所有和CTM002的Class一样的客户

将上面的自联结语句转换成子查询语句

SELECT CustomerNo,Class,CustomerState
FROM Customers
WHERE Class=(
    SELECT Class FROM Customers
    WHERE CustomerNo='CTM002'
);

组合查询UNION和UNION ALL

SELECT CustomerNo,Class,CustomerState
FROM Customers
WHERE Class='C'
UNION
SELECT CustomerNo,Class,CustomerState
FROM Customers
WHERE CustomerState='销售机会'---重复记录不显示

SELECT CustomerNo,Class,CustomerState
FROM Customers
WHERE Class='C'
UNION ALL
SELECT CustomerNo,Class,CustomerState
FROM Customers
WHERE CustomerState='销售机会'
ORDER BY 1,2;--重复记录显示

EXCEPT检索select1中存在select2中不存在的行

SELECT CustomerNo,Class,CustomerState
FROM Customers
WHERE Class='C'
EXCEPT
SELECT CustomerNo,Class,CustomerState
FROM Customers
WHERE CustomerState='销售机会'
ORDER BY 1,2;---检索在select1中存在而在select2中不存在的行

INTERSECT检索两个select语句中都存在的行

SELECT CustomerNo,Class,CustomerState
FROM Customers
WHERE Class='C'
INTERSECT
SELECT CustomerNo,Class,CustomerState
FROM Customers
WHERE CustomerState='销售机会'
ORDER BY 1,2;---检索在两个select语句中都存在的行

插入一条数据INSERT INTO

INSERT INTO Customers(cust_id,
cust_name,
cust_address,
cust_city,
cust_state,
cust_zip,
cust_country,
cust_contact,
cust_email
)
VALUES('2018062501',
'AMY',
'北仑红联渡口路29号',
'宁波',
'OENW',
'28193',
'China',
NULL,
'277816@qq.com'
);
SELECT * FROM Customers;

INSERT INTO 的新用法：插入检索出的数据

INSERT INTO CustNew(
cust_id,
cust_name,
cust_address,
cust_city,
cust_state,
cust_zip,
cust_country,
cust_contact,
cust_email
)
SELECT* FROM Customers;


INSERT INTO CustNew(
cust_id,
cust_name,
cust_address,
cust_city,
cust_state,
cust_zip,
cust_country,
cust_contact,
cust_email
)
SELECT* FROM Customers;

使用INSERT SELECT一次插入多行

INSERT INTO CustNew(
cust_id,
cust_name,
cust_address,
cust_city,
cust_state,
cust_zip,
cust_country,
cust_contact,
cust_email
)
SELECT* FROM Customers--不管SELECT出多少行都会被插入
WHERE NOT cust_id='2018062501';--排除掉已插入的行，不然会提示主键重复，语句结束
SELECT* FROM CustNew;

自动创建一个新表并完全复制另一个表的数据

SELECT* INTO CustCopy
FROM Customers;--这条语句自动创建CustCopy表并将Customers表中的数据完全复制并填充过去

UPDATE更新表中数据

UPDATE CustCopy
SET cust_email='chenlili@intersky.com.cn',
cust_city='广西',
cust_name='陈莉莉'
WHERE cust_id='2018062503';
SELECT *FROM CustCopy;

用表1的数据更新表2的数据

ALTER TABLE CustNew ADD te VARCHAR(20);--在CustNew表中新建te列
UPDATE CustNew SET CustNew.te=CustCopy.cust_name
FROM CustCopy,CustNew
WHERE CustNew.cust_id=CustCopy.cust_id;--用CustCopy表中的cust_name列值更新CustNew表中的te列，条件是两表cust_id相等

删除某个列的值可以将它设置为NULL

UPDATE CustCopy
SET cust_address=NULL
WHERE cust_id='2018062502';
SELECT * FROM CustCopy;

删除表的某一行

DELETE FROM CustCopy
WHERE cust_id='2018062504'

TRUNCATE TABLE删除表

使用TRUNCATE TABLE可以快速删除表中的所有记录，而且无日志记录。与DELETE相比，速度更快，使用的系统资源和事务日志资源更少。
使用DELETE语句，系统一次一行地处理要删除的表中的记录，并在事务处理日志中记录相关删除操作。
使用TRUNCATE TABLE语句一次性完成删除与表有关的所有数据页的操作，且不更新事务处理日志，无法用ROLLBACK回滚。

TRUNCATE TABLE a;--删除表a中的所有数据

创建表

CREATE TABLE Products(
    prod_id CHAR(10) NOT NULL,
    vend_id CHAR(10) NOT NULL,
    prod_name CHAR(254) NOT NULL,
    prod_price DECIMAL(8,2) NOT NULL,
    prod_desc VARCHAR(1000) NULL
);

CREATE TABLE Orders(
    order_num INTEGER NOT NULL,
    order_date DATETIME NOT NULL,
    cust_id CHAR(10) NOT NULL
);

CREATE TABLE Vendors(
    vend_id CHAR(10) NOT NULL,
    vend_name CHAR(50) NOT NULL,
    vend_address CHAR(50),
    vend_city CHAR(50),
    vend_state CHAR(5),
    vend_zip CHAR(10),
    vend_country CHAR(50)
);--不填写NULL和NOT NULL时默认为NULL

新建表并指定默认值DEFAULT

CREATE TABLE OrderItems(
    order_num INTEGER NOT NULL,
    order_item INTEGER NOT NULL,
    prod_id CHAR(10) NOT NULL,
    quantity INTEGER NOT NULL DEFAULT 1,
    item_price DECIMAL(8,2) NOT NULL
);

更新表ALTER TABLE

ALTER TABLE Vendors
ADD vend_phone CHAR(20);
SELECT * FROM Vendors;

ALTER TABLE Vendors
DROP COLUMN vend_phone;

ALTER TABLE Vendors
ADD PRIMARY KEY(vend_id);--给vend_id设置主键

删除整张表及其表结构

DROP TABLE CustNew;

重命名表

EXEC sp_rename 'Orders','testi21';
EXEC sp_rename 'testi21','Orders';

SELECT *FROM Orders;
GO;

创建视图CREATE VIEW view_name AS…

CREATE VIEW ProductCustomers AS
SELECT cust_name,cust_contact,prod_id
FROM Customers,Orders,OrderItems
WHERE Customers.cust_id=Orders.cust_id
AND Orders.order_num=OrderItems.order_num;
GO;

SELECT * FROM ProductCustomers;


SELECT * FROM ProductCustomers
WHERE prod_id='0001';
DROP VIEW ProductCustomers;--删除视图

存储过程（类似自定义函数）

SELECT *FROM Customers;
--输出Customers表中所有cust_contact为空的用户个数,利用存储过程结果应该为2;

CREATE PROCEDURE CusCount
@custc INTEGER OUT--带输出参数的存储过程
AS
SELECT @custc=COUNT(*) FROM Customers
WHERE cust_contact IS NULL;
RETURN @custc;

--新建无参数的存储过程
CREATE PROCEDURE MailingListCount AS
DECLARE @cnt INTEGER
SELECT @cnt=COUNT(*) FROM Customers
WHERE NOT cust_contact IS NULL;
RETURN @cnt;

--调用带输出参数的存储过程
DECLARE @tt INTEGER
EXEC CusCount @tt OUTPUT;
SELECT @tt AS Ccount;
--调用无参数的存储过程
DECLARE @ReturnValue INT
EXEC @ReturnValue=MailingListCount;
SELECT @ReturnValue AS Ccount;

事务处理TRANSACTION

BEGIN TRANSACTION
DELETE FROM Orders;
ROLLBACK TRANSACTION;
GO;
/*
SELECT *FROM Orders;
INSERT INTO Orders VALUES(
'2819','2018-06-25 00:00:00.000','2018062501');
INSERT INTO Orders VALUES(
'2817','2018-06-25 00:00:00.000','2018062502');
INSERT INTO Orders VALUES(
'2818','2018-06-25 00:00:00.000','2018062503');*/

事务处理，COMMIT显式提交

BEGIN TRANSACTION
DELETE FROM Orders WHERE cust_id='2018062501'
DELETE FROM Customers WHERE cust_id='2018062501' 
COMMIT TRANSACTION--这两行语句要不一起提交，要不全部不提交，不存在部分执行完成。

添加保留点SAVE TRANSACTION和回滚至保留点ROLLBACK TRANSACTION

BEGIN TRANSACTION
SELECT *FROM Orders;
DELETE FROM Orders;
INSERT INTO Orders VALUES(
'2819','2018-06-25 00:00:00.000','2018062501');
SAVE TRANSACTION insert1;
INSERT INTO Orders VALUES(
'2817','2018-06-25 00:00:00.000','2018062502');
SAVE TRANSACTION insert2;
INSERT INTO Orders VALUES(
'2818','2018-06-25 00:00:00.000','2018062503');
SAVE TRANSACTION insert3;
ROLLBACK TRANSACTION insert2;--回滚至保留点insert2

游标的定义和使用

DECLARE CustCursor SCROLL CURSOR
FOR
SELECT cust_id FROM Customers
WHERE cust_contact IS NULL;--定义游标CustCursor
OPEN CustCursor;--打开游标

--如何使用一个已打开的游标
DECLARE @cursor CHAR(10);--定义参数cursor
FETCH FIRST FROM CustCursor INTO @cursor;--将游标的值传入该参数
SELECT @cursor AS Cursortest;--将参数输出并取别名为Cursortest

--删除游标
CLOSE CustCursor;
DEALLOCATE CustCursor;--释放游标占用的资源

游标的循环（@@FETCH_STATUS=0）

DECLARE CustCursor SCROLL CURSOR
FOR
SELECT cust_id FROM Customers
WHERE cust_contact IS NULL;
OPEN CustCursor;
DECLARE @cursor1 CHAR(10);
FETCH NEXT FROM CustCursor INTO @cursor1
WHILE (@@FETCH_STATUS=0)--游标的循环
BEGIN
FETCH NEXT FROM CustCursor INTO @cursor1--将游标指向下一个值
END
SELECT @cursor1 AS TT;
--关闭游标并释放资源
CLOSE CustCursor;
DEALLOCATE CustCursor;

主键与外键

ALTER TABLE Products
ADD PRIMARY KEY(prod_id);--用ALTER语句添加主键

ALTER TABLE Orders
ALTER COLUMN cust_id NCHAR(10);--两个表数据类型不同设置外键会报错，因此先更改外键字段的数据类型
--用ALTER设置外键
ALTER TABLE Orders
ADD CONSTRAINT FK_ord--将Orders.cust_id用CONSTRAINT关键字设置唯一约束
FOREIGN KEY(cust_id)
REFERENCES Customers(cust_id)
GO

用ALTER语句设置唯一约束

ALTER TABLE Vendors
ADD UNIQUE(Vend_id);

用ALTER语句设置检查约束

ALTER TABLE Products
ADD CHECK(prod_price>0);

添加索引,系统根据索引快速查询数据

CREATE INDEX prod_name_int
ON Products(prod_name);
SELECT *FROM Products WHERE prod_name='莫匹罗星软膏';
--添加索引后系统能更快检索到数据，索引并不是给使用者用的，而是给系统用的

创建触发器

CREATE TRIGGER cust_state
ON Customers
FOR INSERT,UPDATE
AS
UPDATE Customers
SET cust_state=UPPER(cust_state)
WHERE Customers.cust_id=(SELECT cust_id from inserted);--当Customers.cust_state发生INSERT,UPDATE操作时，触发器将自动把cust_state字段内容从小写变成大写

触发器测试

INSERT INTO Customers(
    cust_id,
    cust_name,
    cust_address,
    cust_city,
    cust_state,
    cust_email
)VALUES(
    '2018062506',
    'Lily',
    '世纪大道333号',
    '北京',
    'ienwoho',
    '783428@qq.com'
);
SELECT *FROM Customers;