本文將分享15個初學(xué)者必看的基礎(chǔ)SQL查詢語句，都很基礎(chǔ)，但是你不一定都會，所以好好看看吧。
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(shè)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(shè)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(guān)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 letrsquo;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(biāo)量函數(shù)
合計函數(shù)和標(biāo)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(dāng)前的日期進(jìn)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(jié)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(jié)合select語句，Order By可以讓查詢結(jié)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(guān)鍵字可以過濾重復(fù)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(jié)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(jié)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(fù)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(dá)式（CTE）——With語句
CTE可以看作是一個臨時的結(jié)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(dá)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(shè)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(fù)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(quán)限進(jìn)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(zhuǎn)列
Pivot可以幫助你實現(xiàn)數(shù)據(jù)行轉(zhuǎn)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)?？吹接腥颂釂柸绾卧赟QL 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(jié)構(gòu)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：
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(dāng)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
以上就是適合初學(xué)者學(xué)習(xí)的基礎(chǔ)SQL查詢語句，希望對大家學(xué)習(xí)SQL查詢語句有所幫助。
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