《SQL必知必会》知识点汇总

Posted 2020-11-20 kukubear0

select CustomerNo from dbo.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

1 select CustomerNo+‘(‘+CustomerState+‘)‘ 
2 AS CustomerTitle
3 from dbo.Customers
4 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

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

排序ORDER BY并以列号指代某一列

1 SELECT CustomerNo,CustomerShortName,CustomerState,Class from dbo.Customers
2 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,SUMD的使用

SELECT AVG(TotalAmount) AS AvgAmount FROM dbo.Inspections;

SELECT COUNT(*) AS CountNum FROM dbo.Customers
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;
SELECT * FROM dbo.Inspections WHERE TotalAmount=‘126000‘

SELECT * FROM dbo.Inspections;
SELECT SUM(TotalVolumn) AS SumV FROM dbo.Inspections;
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

检索在select1中存在而在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;

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,
‘[email protected]‘
);
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

更新表中数据

UPDATE CustCopy
SET cust_email=‘[email protected]‘,
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‘

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;

删除视图

SELECT * FROM ProductCustomers
WHERE prod_id=‘0001‘;
DROP VIEW ProductCustomers;

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;
GO;

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;
GO;

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;
GO;

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;
GO

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

1 DECLARE CustCursor SCROLL CURSOR
2 FOR
3 SELECT cust_id FROM Customers
4 WHERE cust_contact IS NULL;--定义游标CustCursor
5 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

1 CLOSE CustCursor;
2 DEALLOCATE CustCursor;--释放游标占用的资源

游标的滚动实例

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

用ALTER设置外键

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

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‘;
GO;

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‘,
‘[email protected]‘
);
SELECT *FROM Customers;