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15个初学者必看的基础SQL查询语句（转）
译文链接：http://www.codeceo.com/article/15-basic-sql-for-beginner.html
英文原文：Basic SQL Queries for Beginners
1、创建表和数据插入SQL
我们在开始创建数据表和向表中插入演示数据之前，我想给大家解释一下实时数据表的设计理念，这样也许能帮助大家能更好的理解SQL查询。
在数据库设计中，有一条非常重要的规则就是要正确建立主键和外键的关系。
现在我们来创建几个餐厅订单管理的数据表，一共用到3张数据表，Item Master表、Order Master表和Order Detail表。
创建表：
创建Item Master表：
CREATE TABLE [dbo].[ItemMasters]( [Item_Code] [varchar](20) NOT NULL, [Item_Name] [varchar](100) NOT NULL, [Price] Int NOT NULL, [TAX1] Int NOT NULL, [Discount] Int NOT NULL, [Description] [varchar](200) NOT NULL, [IN_DATE] [datetime] NOT NULL, [IN_USR_ID] [varchar](20) NOT NULL, [UP_DATE] [datetime] NOT NULL, [UP_USR_ID] [varchar](20) NOT NULL, CONSTRAINT [PK_ItemMasters] PRIMARY KEY CLUSTERED ( [Item_Code] ASC)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]) ON [PRIMARY]
向Item Master表插入数据：
INSERT INTO [ItemMasters] ([Item_Code],[Item_Name],[Price],[TAX1],[Discount],[Description],[IN_DATE] ,[IN_USR_ID],[UP_DATE],[UP_USR_ID]) VALUES (‘Item001‘,‘Coke‘,55,1,0,‘Coke which need to be cold‘,GETDATE(),‘SHANU‘ ,GETDATE(),‘SHANU‘)INSERT INTO [ItemMasters] ([Item_Code],[Item_Name],[Price],[TAX1],[Discount],[Description],[IN_DATE] ,[IN_USR_ID],[UP_DATE],[UP_USR_ID]) VALUES (‘Item002‘,‘Coffee‘,40,0,2,‘Coffe Might be Hot or Cold user choice‘,GETDATE(),‘SHANU‘ ,GETDATE(),‘SHANU‘)INSERT INTO [ItemMasters] ([Item_Code],[Item_Name],[Price],[TAX1],[Discount],[Description],[IN_DATE] ,[IN_USR_ID],[UP_DATE],[UP_USR_ID]) VALUES (‘Item003‘,‘Chiken Burger‘,125,2,5,‘Spicy‘,GETDATE(),‘SHANU‘ ,GETDATE(),‘SHANU‘)INSERT INTO [ItemMasters] ([Item_Code],[Item_Name],[Price],[TAX1],[Discount],[Description],[IN_DATE] ,[IN_USR_ID],[UP_DATE],[UP_USR_ID]) VALUES (‘Item004‘,‘Potato Fry‘,15,0,0,‘No Comments‘,GETDATE(),‘SHANU‘ ,GETDATE(),‘SHANU‘)
创建Order Master表：
CREATE TABLE [dbo].[OrderMasters]( [Order_No] [varchar](20) NOT NULL, [Table_ID] [varchar](20) NOT NULL, [Description] [varchar](200) NOT NULL, [IN_DATE] [datetime] NOT NULL, [IN_USR_ID] [varchar](20) NOT NULL, [UP_DATE] [datetime] NOT NULL, [UP_USR_ID] [varchar](20) NOT NULL, CONSTRAINT [PK_OrderMasters] PRIMARY KEY CLUSTERED ( [Order_No] ASC)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]) ON [PRIMARY]
向Order Master表插入数据：
INSERT INTO [OrderMasters] ([Order_No],[Table_ID] ,[Description],[IN_DATE],[IN_USR_ID],[UP_DATE],[UP_USR_ID]) VALUES (‘Ord_001‘,‘T1‘,‘‘,GETDATE(),‘SHANU‘ ,GETDATE(),‘SHANU‘)INSERT INTO [OrderMasters] ([Order_No],[Table_ID] ,[Description],[IN_DATE],[IN_USR_ID],[UP_DATE],[UP_USR_ID]) VALUES (‘Ord_002‘,‘T2‘,‘‘,GETDATE(),‘Mak‘ ,GETDATE(),‘MAK‘)INSERT INTO [OrderMasters] ([Order_No],[Table_ID] ,[Description],[IN_DATE],[IN_USR_ID],[UP_DATE],[UP_USR_ID]) VALUES (‘Ord_003‘,‘T3‘,‘‘,GETDATE(),‘RAJ‘ ,GETDATE(),‘RAJ‘)
创建Order Detail表：
CREATE TABLE [dbo].[OrderDetails]( [Order_Detail_No] [varchar](20) NOT NULL, [Order_No] [varchar](20) CONSTRAINT fk_OrderMasters FOREIGN KEY REFERENCES OrderMasters(Order_No), [Item_Code] [varchar](20) CONSTRAINT fk_ItemMasters FOREIGN KEY REFERENCES ItemMasters(Item_Code), [Notes] [varchar](200) NOT NULL, [QTY] INT NOT NULL, [IN_DATE] [datetime] NOT NULL, [IN_USR_ID] [varchar](20) NOT NULL, [UP_DATE] [datetime] NOT NULL, [UP_USR_ID] [varchar](20) NOT NULL, CONSTRAINT [PK_OrderDetails] PRIMARY KEY CLUSTERED ( [Order_Detail_No] ASC)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]) ON [PRIMARY]--Now let’s insert the 3 items for the above Order No ‘Ord_001‘.INSERT INTO [OrderDetails] ([Order_Detail_No],[Order_No],[Item_Code],[Notes],[QTY] ,[IN_DATE],[IN_USR_ID],[UP_DATE],[UP_USR_ID]) VALUES (‘OR_Dt_001‘,‘Ord_001‘,‘Item001‘,‘Need very Cold‘,3 ,GETDATE(),‘SHANU‘ ,GETDATE(),‘SHANU‘)INSERT INTO [OrderDetails] ([Order_Detail_No],[Order_No],[Item_Code],[Notes],[QTY] ,[IN_DATE],[IN_USR_ID],[UP_DATE],[UP_USR_ID]) VALUES (‘OR_Dt_002‘,‘Ord_001‘,‘Item004‘,‘very Hot ‘,2 ,GETDATE(),‘SHANU‘ ,GETDATE(),‘SHANU‘)INSERT INTO [OrderDetails] ([Order_Detail_No],[Order_No],[Item_Code],[Notes],[QTY] ,[IN_DATE],[IN_USR_ID],[UP_DATE],[UP_USR_ID]) VALUES (‘OR_Dt_003‘,‘Ord_001‘,‘Item003‘,‘Very Spicy‘,4 ,GETDATE(),‘SHANU‘ ,GETDATE(),‘SHANU‘)
向Order Detail表插入数据：
INSERT INTO [OrderDetails] ([Order_Detail_No],[Order_No],[Item_Code],[Notes],[QTY] ,[IN_DATE],[IN_USR_ID],[UP_DATE],[UP_USR_ID]) VALUES (‘OR_Dt_004‘,‘Ord_002‘,‘Item002‘,‘Need very Hot‘,2 ,GETDATE(),‘SHANU‘ ,GETDATE(),‘SHANU‘)INSERT INTO [OrderDetails] ([Order_Detail_No],[Order_No],[Item_Code],[Notes],[QTY] ,[IN_DATE],[IN_USR_ID],[UP_DATE],[UP_USR_ID]) VALUES (‘OR_Dt_005‘,‘Ord_002‘,‘Item003‘,‘very Hot ‘,2 ,GETDATE(),‘SHANU‘ ,GETDATE(),‘SHANU‘)INSERT INTO [OrderDetails] ([Order_Detail_No],[Order_No],[Item_Code],[Notes],[QTY] ,[IN_DATE],[IN_USR_ID],[UP_DATE],[UP_USR_ID]) VALUES (‘OR_Dt_006‘,‘Ord_003‘,‘Item003‘,‘Very Spicy‘,4 ,GETDATE(),‘SHANU‘ ,GETDATE(),‘SHANU‘)
2、简单的Select查询语句
Select查询语句是SQL中最基本也是最重要的DML语句之一。那么什么是DML？DML全称Data Manipulation Language（数据操纵语言命令），它可以使用户能够查询数据库以及操作已有数据库中的数据。
下面我们在SQL Server中用select语句来查询我的姓名(Name)：
SELECT ‘My Name Is SYED SHANU‘-- With Column Name using ‘AS‘SELECT ‘My Name Is SYED SHANU‘ as ‘MY NAME‘-- With more then the one Column SELECT ‘My Name‘ as ‘Column1‘, ‘Is‘ as ‘Column2‘, ‘SYED SHANU‘ as ‘Column3‘
在数据表中使用select查询：
-- To Display all the columns from the table we use * operator in select Statement.Select * from ItemMasters-- If we need to select only few fields from a table we can use the Column Name in Select Statement.Select Item_Code ,Item_name as Item ,Price ,Description ,In_DATE FROM ItemMasters
3、合计和标量函数
合计函数和标量函数都是SQL Server的内置函数，我们可以在select查询语句中使用它们，比如Count(), Max(), Sum(), Upper(), lower(), Round()等等。下面我们用SQL代码来解释这些函数的用法：
select * from ItemMasters-- Aggregate-- COUNT() -> returns the Total no of records from table , AVG() returns the Average Value from Colum,MAX() Returns MaX Value from Column-- ,MIN() returns Min Value from Column,SUM() sum of total from ColumnSelect Count(*) TotalRows,AVG(Price) AVGPrice ,MAX(Price) MAXPrice,MIN(Price) MinPrice,Sum(price) PriceTotal FROM ItemMasters-- Scalar -- UCASE() -> Convert to Upper Case ,LCASE() -> Convert to Lower Case,-- SUBSTRING() ->Display selected char from column ->SUBSTRING(ColumnName,StartIndex,LenthofChartoDisplay)--,LEN() -> lenth of column date,-- ROUND() -> Which will round the valueSELECT UPPER(Item_NAME) Uppers,LOWER(Item_NAME) Lowers, SUBSTRING(Item_NAME,2,3) MidValue,LEN(Item_NAME) Lenths ,SUBSTRING(Item_NAME,2,LEN(Item_NAME)) MidValuewithLenFunction, ROUND(Price,0) as Rounded FROM ItemMasters
4、日期函数
在我们的项目数据表中基本都会使用到日期列，因此日期函数在项目中扮演着非常重要的角色。有时候我们对日期函数要非常的小心，它随时可以给你带来巨大的麻烦。在项目中，我们要选择合适的日期函数和日期格式，下面是一些SQL日期函数的例子：
-- GETDATE() -> to Display the Current Date and Time-- Format() -> used to display our date in our requested formatSelect GETDATE() CurrentDateTime, FORMAT(GETDATE(),‘yyyy-MM-dd‘) AS DateFormats, FORMAT(GETDATE(),‘HH-mm-ss‘)TimeFormats, CONVERT(VARCHAR(10),GETDATE(),10) Converts1, CONVERT(VARCHAR(24),GETDATE(),113), CONVERT(NVARCHAR, getdate(), 106) Converts2 ,-- here we used Convert Function REPLACE(convert(NVARCHAR, getdate(), 106), ‘ ‘, ‘/‘) Formats-- Here we used replace and --convert functions. --first we convert the date to nvarchar and then we replace the ‘‘ with ‘/‘ select * from ItemmastersSelect ITEM_NAME,IN_DATE CurrentDateTime, FORMAT(IN_DATE,‘yyyy-MM-dd‘) AS DateFormats, FORMAT(IN_DATE,‘HH-mm-ss‘)TimeFormats, CONVERT(VARCHAR(10),IN_DATE,10) Converts1, CONVERT(VARCHAR(24),IN_DATE,113), convert(NVARCHAR, IN_DATE, 106) Converts2 ,-- here we used Convert Function REPLACE(convert(NVARCHAR,IN_DATE, 106), ‘ ‘, ‘/‘) Formats FROM Itemmasters
DatePart –> 该函数可以获取年、月、日的信息。
DateADD –> 该函数可以对当前的日期进行加减。
DateDiff –> 该函数可以比较2个日期。
--Datepart DATEPART(dateparttype,yourDate)SELECT DATEPART(yyyy,getdate()) AS YEARs ,DATEPART(mm,getdate()) AS MONTHS,DATEPART(dd,getdate()) AS Days,DATEPART(week,getdate()) AS weeks,DATEPART(hour,getdate()) AS hours--Days Add to add or subdtract date from a selected date.SELECT GetDate()CurrentDate,DATEADD(day,12,getdate()) AS AddDays , DATEADD(day,-4,getdate()) AS FourDaysBeforeDate -- DATEDIFF() -> to display the Days between 2 dates select DATEDIFF(year,‘2003-08-05‘,getdate()) yearDifferance , DATEDIFF(day,DATEADD(day,-24,getdate()),getdate()) daysDifferent, DATEDIFF(month,getdate(),DATEADD(Month,6,getdate())) MonthDifferance
5、其他Select函数
Top —— 结合select语句，Top函数可以查询头几条和末几条的数据记录。
Order By —— 结合select语句，Order By可以让查询结果按某个字段正序和逆序输出数据记录。
--Top to Select Top first and last records using Select Statement.Select * FROM ItemMasters--> First Display top 2 RecordsSelect TOP 2 Item_Code ,Item_name as Item ,Price ,Description ,In_DATEFROM ItemMasters--> to Display the Last to Records we need to use the Order By Clause-- order By to display Records in assending or desending order by the columnsSelect TOP 2 Item_Code ,Item_name as Item ,Price ,Description ,In_DATEFROM ItemMastersORDER BY Item_Code DESC
Distinct —— distinct关键字可以过滤重复的数据记录。
Select * FROM ItemMasters--Distinct -> To avoid the Duplicate records we use the distinct in select statement-- for example in this table we can see here we have the duplicate record ‘Chiken Burger‘-- but with different Item_Code when i use the below select statement see what happenSelect Item_name as Item ,Price ,Description ,IN_USR_ID FROM ItemMasters-- here we can see the Row No 3 and 5 have the duplicate record to avoid this we use the distinct Keyword in select statement.select Distinct Item_name as Item ,Price ,Description ,IN_USR_ID FROM ItemMasters
Where子句在SQL Select查询语句中非常重要，为什么要使用where子句？什么时候使用where子句？where子句是利用一些条件来过滤数据结果集。
下面我们从10000条数据记录中查询Order_No为某个值或者某个区间的数据记录，另外还有其他的条件。
Select * from ItemMastersSelect * from OrderDetails--Where -> To display the data with certain conditions-- Now below example which will display all the records which has Item_Name=‘Coke‘select * FROM ItemMasters WHERE ITEM_NAME=‘COKE‘-- If we want display all the records Iten_Name which Starts with ‘C‘ then we use Like in where clause.SELECT * FROM ItemMasters WHERE ITEM_NAME Like ‘C%‘--> here we display the ItemMasters where the price will be greater then or equal to 40.--> to use more then one condition we can Use And or Or operator.--If we want to check the data between to date range then we can use Between Operator in Where Clause.select Item_name as Item ,Price ,Description ,IN_USR_ID FROM ItemMasters WHERE ITEM_NAME Like ‘C%‘ AND price >=40--> here we display the OrderDetails where the Qty will be greater 3Select * FROM OrderDetails WHERE qty>3
Where – In 子句
-- In clause -> used to display the data which is in the conditionselect * FROM ItemMasters WHERE Item_name IN (‘Coffee‘,‘Chiken Burger‘)-- In clause with Order By - Here we display the in descending order.select * FROM ItemMasters WHERE Item_name IN (‘Coffee‘,‘Chiken Burger‘) ORDER BY Item_Code Desc
Where – Between子句
-- between -> Now if we want to display the data between to date range then we use betweeen keywordselect * FROM ItemMastersselect * FROM ItemMasters WHERE In_Date BETWEEN ‘2014-09-22 15:59:02.853‘ AND ‘2014-09-22 15:59:02.853‘select * FROM ItemMasters WHERE ITEM_NAME Like ‘C%‘ AND In_Date BETWEEN ‘2014-09-22 15:59:02.853‘ AND ‘2014-09-22 15:59:02.853‘
查询某个条件区间的数据，我们常常使用between子句。
7、Group By 子句
Group By子句可以对查询的结果集按指定字段分组：
--Group By -> To display the data with group result.Here we can see we display all the AQggregate result by Item NameSelect ITEM_NAME,Count(*) TotalRows,AVG(Price) AVGPrice ,MAX(Price) MAXPrice,MIN(Price) MinPrice,Sum(price) PriceTotal FROM ItemMasters GROUP BY ITEM_NAME-- Here this group by will combine all the same Order_No result and make the total or each order_NOSelect Order_NO,Sum(QTy) as TotalQTY FROM OrderDetails where qty>=2 GROUP BY Order_NO-- Here the Total will be created by order_No and Item_CodeSelect Order_NO,Item_Code,Sum(QTy) as TotalQTY FROM OrderDetails where qty>=2 GROUP BY Order_NO,Item_Code Order By Order_NO Desc,Item_Code
Group By & Having 子句
--Group By Clause -- here this will display all the Order_no Select Order_NO,Sum(QTy) as TotalQTY FROM OrderDetails GROUP BY Order_NO-- Having Clause-- This will avoid the the sum(qty) less then 4 Select Order_NO,Sum(QTy) as TotalQTY FROM OrderDetails GROUP BY Order_NO HAVING Sum(QTy) >4
8、子查询
子查询一般出现在where内连接查询和嵌套查询中，select、update和delete语句中均可以使用。
--Sub Query -- Here we used the Sub query in where clause to get all the Item_Code where the price>40 now this sub --query reslut we used in our main query to filter all the records which Item_code from Subquery resultSELECT * FROM ItemMasters WHERE Item_Code IN (SELECT Item_Code FROM ItemMasters WHERE price > 40) -- Sub Query with Insert StatementINSERT INTO ItemMasters ([Item_Code] ,[Item_Name],[Price],[TAX1],[Discount],[Description],[IN_DATE] ,[IN_USR_ID],[UP_DATE] ,[UP_USR_ID]) Select ‘Item006‘ ,Item_Name,Price+4,TAX1,Discount,Description ,GetDate(),‘SHANU‘,GetDate(),‘SHANU‘ from ItemMasters where Item_code=‘Item002‘ --After insert we can see the result as Select * from ItemMasters
9、连接查询
到目前为止我们接触了不少单表的查询语句，现在我们来使用连接查询获取多个表的数据。
简单的join语句：
--Now we have used the simple join with out any condition this will display all the-- records with duplicate data to avaoid this we see our next example with conditionSELECT * FROM Ordermasters,OrderDetails-- Simple Join with Condition now here we can see the duplicate records now has been avoided by using the where checing with both table primaryKey fieldSELECT * FROM Ordermasters as M, OrderDetails as D where M.Order_NO=D.Order_NO and M.Order_NO=‘Ord_001‘-- Now to make more better understanding we need to select the need fields from both --table insted of displaying all column.SELECT M.order_NO,M.Table_ID,D.Order_detail_no,Item_code,Notes,Qty FROM Ordermasters as M, OrderDetails as D where M.Order_NO=D.Order_NO -- Now lets Join 3 table SELECT M.order_NO,M.Table_ID,D.Order_detail_no,I.Item_Name,D.Notes,D.Qty,I.Price, I.Price*D.Qty as TotalPrice FROM Ordermasters as M, OrderDetails as D,ItemMasters as I where M.Order_NO=D.Order_NO AND D.Item_Code=I.Item_Code
Inner Join,Left Outer Join,Right Outer Join and Full outer Join
下面是各种类型的连接查询代码：
--INNER JOIN --This will display the records which in both table Satisfy here i have used Like in where class which display the SELECT M.order_NO,M.Table_ID,D.Order_detail_no,I.Item_Name,D.Notes,D.Qty,I.Price,I.Price*D.Qty as TotalPrice FROM Ordermasters as M Inner JOIN OrderDetails as D ON M.Order_NO=D.Order_NO INNER JOIN ItemMasters as I ON D.Item_Code=I.Item_Code WHERE M.Table_ID like ‘T%‘--LEFT OUTER JOIN --This will display the records which Left side table Satisfy SELECT M.order_NO,M.Table_ID,D.Order_detail_no,I.Item_Name,D.Notes,D.Qty,I.Price,I.Price*D.Qty as TotalPrice FROM Ordermasters as M LEFT OUTER JOIN OrderDetails as D ON M.Order_NO=D.Order_NO LEFT OUTER JOIN ItemMasters as I ON D.Item_Code=I.Item_Code WHERE M.Table_ID like ‘T%‘--RIGHT OUTER JOIN --This will display the records which Left side table Satisfy SELECT M.order_NO,M.Table_ID,D.Order_detail_no,I.Item_Name,D.Notes,D.Qty,I.Price,I.Price*D.Qty as TotalPrice FROM Ordermasters as M RIGHT OUTER JOIN OrderDetails as D ON M.Order_NO=D.Order_NO RIGHT OUTER JOIN ItemMasters as I ON D.Item_Code=I.Item_Code WHERE M.Table_ID like ‘T%‘--FULL OUTER JOIN --This will display the records which Left side table Satisfy SELECT M.order_NO,M.Table_ID,D.Order_detail_no,I.Item_Name,D.Notes,D.Qty,I.Price,I.Price*D.Qty as TotalPrice FROM Ordermasters as M FULL OUTER JOIN OrderDetails as D ON M.Order_NO=D.Order_NO FULL OUTER JOIN ItemMasters as I ON D.Item_Code=I.Item_Code WHERE M.Table_ID like ‘T%‘
10、Union合并查询
Union查询可以把多张表的数据合并起来，Union只会把唯一的数据查询出来，而Union ALL则会把重复的数据也查询出来。
Select column1,Colum2 from Table1UnionSelect Column1,Column2 from Table2Select column1,Colum2 from Table1Union AllSelect Column1,Column2 from Table2
具体的例子如下：
--Select with different where condition which display the result as 2 Table resultselect Item_Code,Item_Name,Price,Description FROM ItemMasters where price <=44select Item_Code,Item_Name,Price,Description FROM ItemMasters where price >44-- Union with same table but with different where condition now which result as one table which combine both the result.select Item_Code,Item_Name,Price,Description FROM ItemMasters where price <=44UNIONselect Item_Code,Item_Name,Price,Description FROM ItemMasters where price >44-- Union ALL with Join sample SELECT M.order_NO,M.Table_ID,D.Order_detail_no,I.Item_Name,D.Notes,D.Qty,I.Price,I.Price*D.Qty as TotalPrice FROM Ordermasters as M (NOLOCK) Inner JOIN OrderDetails as D ON M.Order_NO=D.Order_NO INNER JOIN ItemMasters as I ON D.Item_Code=I.Item_Code WHERE I.Price <=44 Union ALL SELECT M.order_NO,M.Table_ID,D.Order_detail_no,I.Item_Name,D.Notes,D.Qty,I.Price,I.Price*D.Qty as TotalPrice FROM Ordermasters as M (NOLOCK) Inner JOIN OrderDetails as D ON M.Order_NO=D.Order_NO INNER JOIN ItemMasters as I ON D.Item_Code=I.Item_Code WHERE I.Price>44
11、公用表表达式（CTE）——With语句
CTE可以看作是一个临时的结果集，可以在接下来的一个SELECT,INSERT,UPDATE,DELETE,MERGE语句中被多次引用。使用公用表达式可以让语句更加清晰简练。
declare @sDate datetime, @eDate datetime;select @sDate = getdate()-5, @eDate = getdate()+16;--select @sDate StartDate,@eDate EndDate;with cte as ( select @sDate StartDate,‘W‘+convert(varchar(2), DATEPART( wk, @sDate))+‘(‘+convert(varchar(2),@sDate,106)+‘)‘ as ‘SDT‘ union all select dateadd(DAY, 1, StartDate) , ‘W‘+convert(varchar(2),DATEPART( wk, StartDate))+‘(‘+convert(varchar(2), dateadd(DAY, 1, StartDate),106)+‘)‘ as ‘SDT‘ FROM cte WHERE dateadd(DAY, 1, StartDate)<= @eDate )select * from cteoption (maxrecursion 0)
12、视图
很多人对视图View感到很沮丧，因为它看起来跟select语句没什么区别。在视图中我们同样可以使用select查询语句，但是视图对我们来说依然非常重要。
假设我们要联合查询4张表中的20几个字段，那么这个select查询语句会非常复杂。但是这样的语句我们在很多地方都需要用到，如果将它编写成视图，那么使用起来会方便很多。利用视图查询有以下几个优点：
- 一定程度上提高查询速度
- 可以对一些字段根据不同的权限进行屏蔽，因此提高了安全性
- 对多表的连接查询会非常方便
下面是一个视图的代码例子：
CREATE VIEW viewnameASSelect ColumNames from yourTableExample : -- Here we create view for our Union ALL exampleCreate VIEW myUnionVIEWAS SELECT M.order_NO,M.Table_ID,D.Order_detail_no,I.Item_Name,D.Notes,D.Qty,I.Price, I.Price*D.Qty as TotalPrice FROM Ordermasters as M Inner JOIN OrderDetails as D ON M.Order_NO=D.Order_NO INNER JOIN ItemMasters as I ON D.Item_Code=I.Item_Code WHERE I.Price <=44 Union ALL SELECT M.order_NO,M.Table_ID,D.Order_detail_no,I.Item_Name,D.Notes,D.Qty,I.Price, I.Price*D.Qty as TotalPrice FROM Ordermasters as M Inner JOIN OrderDetails as D ON M.Order_NO=D.Order_NO INNER JOIN ItemMasters as I ON D.Item_Code=I.Item_Code WHERE I.Price>44-- View Select querySelect * from myUnionVIEW-- We can also use the View to display with where condition and with selected fields Select order_Detail_NO,Table_ID,Item_Name,Price from myUnionVIEW where price >40
13、Pivot行转列
Pivot可以帮助你实现数据行转换成数据列，具体用法如下：
-- Simple Pivot Example SELECT * FROM ItemMasters PIVOT(SUM(Price) FOR ITEM_NAME IN ([Chiken Burger], Coffee,Coke)) AS PVTTable-- Pivot with detail exampleSELECT *FROM ( SELECT ITEM_NAME, price as TotAmount FROM ItemMasters) as sPIVOT( SUM(TotAmount) FOR [ITEM_NAME] IN ([Chiken Burger], [Coffee],[Coke]))AS MyPivot
14、存储过程
我经常看到有人提问如何在SQL Server中编写多条查询的SQL语句，然后将它们使用到C#程序中去。存储过程就可以完成这样的功能，存储过程可以将多个SQL查询聚集在一起，创建存储过程的基本结构是这样的：
CREATE PROCEDURE [ProcedureName] AS BEGIN-- Select or Update or Insert query.ENDTo execute SP we useexec ProcedureName
创建一个没有参数的存储过程：
-- ============================================= -- Author : Shanu -- Create date : 2014-09-15 -- Description : To Display Pivot Data -- Latest -- Modifier : Shanu -- Modify date : 2014-09-15 -- ============================================= -- exec USP_SelectPivot -- ============================================= Create PROCEDURE [dbo].[USP_SelectPivot] AS BEGIN DECLARE @MyColumns AS NVARCHAR(MAX), @SQLquery AS NVARCHAR(MAX)-- here first we get all the ItemName which should be display in Columns we use this in our necxt pivot queryselect @MyColumns = STUFF((SELECT ‘,‘ + QUOTENAME(Item_NAME) FROM ItemMasters GROUP BY Item_NAME ORDER BY Item_NAME FOR XML PATH(‘‘), TYPE ).value(‘.‘, ‘NVARCHAR(MAX)‘) ,1,1,‘‘)-- here we use the above all Item name to disoplay its price as column and row displayset @SQLquery = N‘SELECT ‘ + @MyColumns + N‘ from ( SELECT ITEM_NAME, price as TotAmount FROM ItemMasters ) x pivot ( SUM(TotAmount) for ITEM_NAME in (‘ + @MyColumns + N‘) ) p ‘exec sp_executesql @SQLquery; RETURN END
15、函数Function
之前我们介绍了MAX(),SUM(), GetDate()等最基本的SQL函数，现在我们来看看如何创建自定义SQL函数。创建函数的格式如下：
Create Function functionNameAsBeginEND
下面是一个简单的函数示例：
-- ============================================= -- Author : Shanu -- Create date : 2014-09-15 -- Description : To Display Pivot Data -- Latest -- Modifier : Shanu -- Modify date : 2014-09-15 Alter FUNCTION [dbo].[ufnSelectitemMaster]()RETURNS int AS -- Returns total Row count of Item Master.BEGIN DECLARE @RowsCount AS int;Select @RowsCount= count(*)+1 from ItemMasters RETURN @RowsCount;END-- to View Function we use select and fucntion Nameselect [dbo].[ufnSelectitemMaster]()
下面的一个函数可以实现从给定的日期中得到当前月的最后一天：
-- ============================================= -- Author : Shanu -- Create date : 2014-09-15 -- Description : To Display Pivot Data -- Latest -- Modifier : Shanu -- Modify date : 2014-09-15 ALTER FUNCTION [dbo].[ufn_LastDayOfMonth]( @DATE NVARCHAR(10) )RETURNS NVARCHAR(10)ASBEGIN RETURN CONVERT(NVARCHAR(10), DATEADD(D, -1, DATEADD(M, 1, CAST(SUBSTRING(@DATE,1,7) + ‘-01‘ AS DATETIME))), 120)ENDSELECT dbo.ufn_LastDayOfMonth(‘2014-09-01‘)AS LastDay
15个初学者必看的基础SQL查询语句（转）
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