1、創(chuàng)建表和數(shù)據(jù)插入SQL
我們在開始創(chuàng)建數(shù)據(jù)表和向表中插入演示數(shù)據(jù)之前，我想給大家解釋一下實時數(shù)據(jù)表的設計理念，這樣也許能幫助大家能更好的理解SQL查詢。
在數(shù)據(jù)庫設計中，有一條非常重要的規(guī)則就是要正確建立主鍵和外鍵的關系。
現(xiàn)在我們來創(chuàng)建幾個餐廳訂單管理的數(shù)據(jù)表，一共用到3張數(shù)據(jù)表，Item Master表、Order Master表和Order Detail表。
創(chuàng)建表：
創(chuàng)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表插入數(shù)據(jù)：
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')
創(chuàng)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表插入數(shù)據(jù)：
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')
創(chuàng)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表插入數(shù)據(jù)：
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、簡單的Select查詢語句
Select查詢語句是SQL中最基本也是最重要的DML語句之一。那么什么是DML？DML全稱Data Manipulation Language（數(shù)據(jù)操縱語言命令），它可以使用戶能夠查詢數(shù)據(jù)庫以及操作已有數(shù)據(jù)庫中的數(shù)據(jù)。
下面我們在SQL Server中用select語句來查詢我的姓名(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'
在數(shù)據(jù)表中使用select查詢：
-- 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、合計和標量函數(shù)
合計函數(shù)和標量函數(shù)都是SQL Server的內(nèi)置函數(shù)，我們可以在select查詢語句中使用它們，比如Count(), Max(), Sum(), Upper(), lower(), Round()等等。下面我們用SQL代碼來解釋這些函數(shù)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 Column Select 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 value SELECT 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、日期函數(shù)
在我們的項目數(shù)據(jù)表中基本都會使用到日期列，因此日期函數(shù)在項目中扮演著非常重要的角色。有時候我們對日期函數(shù)要非常的小心，它隨時可以給你帶來巨大的麻煩。在項目中，我們要選擇合適的日期函數(shù)和日期格式，下面是一些SQL日期函數(shù)的例子：
-- GETDATE() -> to Display the Current Date and Time -- Format() -> used to display our date in our requested format Select 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 Itemmasters Select 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 –> 該函數(shù)可以獲取年、月、日的信息。
DateADD –> 該函數(shù)可以對當前的日期進行加減。
DateDiff –> 該函數(shù)可以比較2個日期。
--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函數(shù)
Top —— 結合select語句，Top函數(shù)可以查詢頭幾條和末幾條的數(shù)據(jù)記錄。
Order By —— 結合select語句，Order By可以讓查詢結果按某個字段正序和逆序輸出數(shù)據(jù)記錄。
--Top to Select Top first and last records using Select Statement. Select * FROM ItemMasters --> First Display top 2 Records Select TOP 2 Item_Code
,Item_name as Item
,Price
,Description
,In_DATE FROM 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 columns Select TOP 2 Item_Code
,Item_name as Item
,Price
,Description
,In_DATE FROM ItemMasters ORDER BY Item_Code DESC
Distinct —— distinct關鍵字可以過濾重復的數(shù)據(jù)記錄。
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 happen Select 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
6、Where子句
Where子句在SQL Select查詢語句中非常重要，為什么要使用where子句？什么時候使用where子句？where子句是利用一些條件來過濾數(shù)據(jù)結果集。
下面我們從10000條數(shù)據(jù)記錄中查詢Order_No為某個值或者某個區(qū)間的數(shù)據(jù)記錄，另外還有其他的條件。
Select * from ItemMasters Select * 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 3 Select * FROM OrderDetails WHERE qty>3
Where – In 子句
-- In clause -> used to display the data which is in the condition select * 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 keyword select * FROM ItemMasters select * 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'
查詢某個條件區(qū)間的數(shù)據(jù)，我們常常使用between子句。
7、Group By 子句
Group By子句可以對查詢的結果集按指定字段分組：
--Group By -> To display the data with group result.Here we can see we display all the AQggregate result by Item Name Select 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_NO Select 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_Code Select 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、子查詢
子查詢一般出現(xiàn)在where內(nèi)連接查詢和嵌套查詢中，select、update和delete語句中均可以使用。
--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 result SELECT * FROM ItemMasters WHERE Item_Code IN (SELECT Item_Code FROM ItemMasters WHERE price > 40) -- Sub Query with Insert Statement INSERT 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、連接查詢
到目前為止我們接觸了不少單表的查詢語句，現(xiàn)在我們來使用連接查詢獲取多個表的數(shù)據(jù)。
簡單的join語句：
--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 condition SELECT * 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 field SELECT * 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
下面是各種類型的連接查詢代碼：
--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合并查詢
Union查詢可以把多張表的數(shù)據(jù)合并起來，Union只會把唯一的數(shù)據(jù)查詢出來，而Union ALL則會把重復的數(shù)據(jù)也查詢出來。
Select column1,Colum2 from Table1 Union Select Column1,Column2 from Table2 Select column1,Colum2 from Table1 Union All Select Column1,Column2 from Table2
具體的例子如下：
--Select with different where condition which display the result as 2 Table result select Item_Code,Item_Name,Price,Description FROM ItemMasters where price <=44 select 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 <=44 UNION select 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、公用表表達式（CTE）——With語句
CTE可以看作是一個臨時的結果集，可以在接下來的一個SELECT,INSERT,UPDATE,DELETE,MERGE語句中被多次引用。使用公用表達式可以讓語句更加清晰簡練。
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 cte option (maxrecursion 0)
12、視圖
很多人對視圖View感到很沮喪，因為它看起來跟select語句沒什么區(qū)別。在視圖中我們同樣可以使用select查詢語句，但是視圖對我們來說依然非常重要。
假設我們要聯(lián)合查詢4張表中的20幾個字段，那么這個select查詢語句會非常復雜。但是這樣的語句我們在很多地方都需要用到，如果將它編寫成視圖，那么使用起來會方便很多。利用視圖查詢有以下幾個優(yōu)點：
一定程度上提高查詢速度
可以對一些字段根據(jù)不同的權限進行屏蔽，因此提高了安全性
對多表的連接查詢會非常方便
下面是一個視圖的代碼例子：
CREATE VIEW viewname AS Select ColumNames from yourTable
Example : -- Here we create view for our Union ALL example Create VIEW myUnionVIEW AS 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 query Select * 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行轉列
Pivot可以幫助你實現(xiàn)數(shù)據(jù)行轉換成數(shù)據(jù)列，具體用法如下：
-- Simple Pivot Example SELECT * FROM ItemMasters PIVOT(SUM(Price) FOR ITEM_NAME IN ([Chiken Burger], Coffee,Coke)) AS PVTTable -- Pivot with detail example SELECT * FROM ( SELECT ITEM_NAME,
price as TotAmount FROM ItemMasters
) as s PIVOT ( SUM(TotAmount) FOR [ITEM_NAME] IN ([Chiken Burger], [Coffee],[Coke])
)AS MyPivot
14、存儲過程
我經(jīng)常看到有人提問如何在SQL Server中編寫多條查詢的SQL語句，然后將它們使用到C#程序中去。存儲過程就可以完成這樣的功能，存儲過程可以將多個SQL查詢聚集在一起，創(chuàng)建存儲過程的基本結構是這樣的：
CREATE PROCEDURE [ProcedureName] AS BEGIN -- Select or Update or Insert query. END To execute SP we use exec ProcedureName
創(chuàng)建一個沒有參數(shù)的存儲過程：
-- ============================================= -- 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 query select @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 display set @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、函數(shù)Function
之前我們介紹了MAX(),SUM(), GetDate()等最基本的SQL函數(shù)，現(xiàn)在我們來看看如何創(chuàng)建自定義SQL函數(shù)。創(chuàng)建函數(shù)的格式如下：
Create Function functionName As Begin END
下面是一個簡單的函數(shù)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 Name
select [dbo].[ufnSelectitemMaster]()
下面的一個函數(shù)可以實現(xiàn)從給定的日期中得到當前月的最后一天：
-- ============================================= -- 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) AS BEGIN RETURN CONVERT(NVARCHAR(10), DATEADD(D, -1, DATEADD(M, 1, CAST(SUBSTRING(@DATE,1,7) + '-01' AS DATETIME))), 120) END SELECT dbo.ufn_LastDayOfMonth('2014-09-01')AS LastDay
