时间:2021-07-01 10:21:17 帮助过:55人阅读
本文将分享15个初学者必看的基础SQL查询语句,都很基础,但是你不一定都会,所以好好看看吧。
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 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 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 –> 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 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 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 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 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 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 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 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 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:
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 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 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.
- 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
- 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 functionName
- As
- Begin
- END
下面是一个简单的函数示例:
- 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:
- 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
以上就是适合初学者学习的基础SQL查询语句,希望对大家学习SQL查询语句有所帮助。