15个初学者必看的基础SQL查询语句

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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：

? 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 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：

 

? 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 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：

? 1 2 3 4 5 6 7 8 9 10 11 12 13 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：

? 1 2 3 4 5 6 7 8 9 10 11 12 13 14 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：

 

? 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 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：

? 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 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)：

? 1 2 3 4 5 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：

? 1 2 3 4 5 6 7 8 9 10 -- 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：

? 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 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：

? 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 -- 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。

 

? 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 --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。

? 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 --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。

? 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 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。

? 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 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

? 1 2 3 4 5 6 7 8 9 10 11 12 -- 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

? 1 2 3 4 5 6 7 8 9 10 11 12 -- 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：

? 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 --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

? 1 2 3 4 5 6 7 8 9 10 --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。

 

? 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 --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：

 

? 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 --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：

 

? 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 --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。

 

? 1 2 3 4 5 6 7 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：

 

? 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 --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。

 

? 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 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：

 

? 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 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：

? 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 -- 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：

 

? 1 2 3 4 5 6 7 8 9 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：

 

? 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 -- =============================================                                -- 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：

? 1 2 3 4 Create Function functionName As Begin END

下面是一个简单的函数示例：                                                 

 

? 1 2 3 4 5 6 7 8 9 10 11 12 13 14 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：

? 1 2 3 4 5 6 7 8 9 10 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。