15 grundlegende SQL-Abfrageanweisungen, die Anfänger lesen müssen
- 伊谢尔伦Original
- 2016-11-24 10:56:581091Durchsuche
1. Erstellen Sie eine Tabelle und fügen Sie Daten in SQL ein
Bevor wir mit der Erstellung einer Datentabelle und dem Einfügen von Demodaten in die Tabelle beginnen, möchte ich Ihnen das Designkonzept der Echtzeit erklären Datentabelle, die Ihnen helfen kann, SQL-Abfragen besser zu verstehen.
Beim Datenbankdesign ist es eine sehr wichtige Regel, die Beziehung zwischen Primärschlüsseln und Fremdschlüsseln korrekt herzustellen.
Jetzt erstellen wir mehrere Datentabellen für die Auftragsverwaltung im Restaurant. Insgesamt werden drei Datentabellen verwendet: die Artikelstammtabelle, die Bestellstammtabelle und die Bestelldetailtabelle.
Tabelle erstellen:
Artikelstammtabelle erstellen:
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]
Daten in Artikelstammtabelle einfügen:
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')Bestellstammtabelle erstellen:
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]
Daten in die Tabelle „Bestellstamm“ einfügen:
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')Tabelle „Bestelldetails“ erstellen:
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')Daten in die Tabelle „Bestelldetails“ einfügen:
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. Einfache Select-Abfrageanweisung
Die Select-Abfrageanweisung ist eine der grundlegendsten und wichtigsten DML-Anweisungen in SQL. Was ist DML? DML steht für Data Manipulation Language (Datenmanipulationssprache), die es Benutzern ermöglicht, Datenbanken abzufragen und Daten in vorhandenen Datenbanken zu manipulieren.
Als nächstes verwenden wir die Select-Anweisung in SQL Server, um meinen Namen (Name) abzufragen:
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'
Verwenden Sie die Select-Abfrage in der Datentabelle:
-- 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. Gesamt- und Skalarfunktionen
Gesamtfunktionen und Skalarfunktionen sind integrierte Funktionen von SQL Server. Wir können sie in ausgewählten Abfrageanweisungen verwenden, z. B. Count(), Max(), Sum(), Upper ( ), Lower(), Round() usw. Nachfolgend verwenden wir SQL-Code, um die Verwendung dieser Funktionen zu erläutern:
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 ItemMasters4. Datumsfunktion
Die Datumsspalte wird grundsätzlich in unserer Projektdatentabelle verwendet, daher wird die Datumsfunktion verwendet spielt im Projekt eine sehr wichtige Rolle. Manchmal müssen wir mit Datumsfunktionen sehr vorsichtig sein, sie können Ihnen jederzeit große Probleme bereiten. Im Projekt müssen wir die entsprechende Datumsfunktion und das Datumsformat auswählen. Hier sind einige Beispiele für SQL-Datumsfunktionen:
-- 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 –> .
DateADD –> Diese Funktion kann das aktuelle Datum addieren und subtrahieren.
DateDiff –> Diese Funktion kann zwei Daten vergleichen.
--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. Andere Select-Funktionen
Top – In Kombination mit der Select-Anweisung kann die Top-Funktion die ersten und letzten paar Datensätze abfragen.
Sortieren nach – In Kombination mit der Select-Anweisung ermöglicht „Order By“ den Abfrageergebnissen, Datensätze in positiver und umgekehrter Reihenfolge eines bestimmten Felds auszugeben.
-
-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 – Das Schlüsselwort „distinct“ kann doppelte Datensätze filtern.
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-Klausel
Die Where-Klausel ist in der SQL Select-Abfrageanweisung sehr wichtig. Warum die Where-Klausel verwenden? Wann sollte die Where-Klausel verwendet werden? Die where-Klausel verwendet einige Bedingungen, um die Datenergebnismenge zu filtern.
Als nächstes fragen wir die Datensätze ab, deren Order_No ein bestimmter Wert oder ein bestimmter Bereich aus 10.000 Datensätzen ist, und es gibt weitere Bedingungen.
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-Klausel
-- 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-Klausel
-- 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'
Um Daten in einem bestimmten Bedingungsbereich abzufragen, verwenden wir häufig die Between-Klausel Satz.
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 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 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 ItemMasters9、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 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_CodeInner 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 Table1 Union Select Column1,Column2 from Table2 Select column1,Colum2 from Table1 Union All Select Column1,Column2 from Table2
具体的例子如下：
--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 WHEREI.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_NOINNER JOIN ItemMasters as I ON D.Item_Code=I.Item_CodeWHEREI.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 cte
option (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 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 WHEREI.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_CodeWHEREI.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 >4013、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 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 MyPivot14、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. END To execute SP we use exec 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 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
END15、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 functionName As Begin END
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 Name select [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) 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
Stellungnahme：
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