1. 程式人生 > >15個初學者必看的基礎SQL查詢語句

15個初學者必看的基礎SQL查詢語句

1、建立表和資料插入SQL

我們在開始建立資料表和向表中插入演示資料之前,我想給大家解釋一下實時資料表的設計理念,這樣也許能幫助大家能更好的理解SQL查詢。

在資料庫設計中,有一條非常重要的規則就是要正確建立主鍵和外來鍵的關係。

現在我們來建立幾個餐廳訂單管理的資料表,一共用到3張資料表,Item Master表、Order Master表和Order Detail表。

建立表:

建立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表插入資料:

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')

建立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表插入資料:

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')

建立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表插入資料:

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。那麼什麼是DML?DML全稱Data Manipulation Language(資料操縱語言命令),它可以使使用者能夠查詢資料庫以及操作已有資料庫中的資料。

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'

在資料表中使用select查詢:

-- To Display all the columns from the table we use * operator in select Statement.
Select * from ItemMasters
-- If we need to select only few fields from a table we can use the Column Name in Select Statement.
Select    Item_Code
		,Item_name as Item
		,Price
		,Description
		,In_DATE
		FROM
		ItemMasters

3、合計和標量函式

合計函式和標量函式都是SQL Server的內建函式,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程式碼來解釋這些函式的用法:

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、日期函式

在我們的專案資料表中基本都會使用到日期列,因此日期函式在專案中扮演著非常重要的角色。有時候我們對日期函式要非常的小心,它隨時可以給你帶來巨大的麻煩。在專案中,我們要選擇合適的日期函式和日期格式,下面是一些SQL日期函式的例子:

-- 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 –>  該函式可以獲取年、月、日的資訊。

DateADD –>  該函式可以對當前的日期進行加減。

DateDiff  –>  該函式可以比較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函式

Top —— 結合select語句,Top函式可以查詢頭幾條和末幾條的資料記錄。

Order By —— 結合select語句,Order By可以讓查詢結果按某個欄位正序和逆序輸出資料記錄。

--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
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,為什麼要使用where子句?什麼時候使用where子句?where子句是利用一些條件來過濾資料結果集。

下面我們從10000條資料記錄中查詢Order_No為某個值或者某個區間的資料記錄,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'

查詢某個條件區間的資料,我們常常使用between子句。

7、Group By 子句

Group By子句可以對查詢的結果集按指定欄位分組:

--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

子查詢一般出現在where內連線查詢和巢狀查詢中,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、連線查詢

到目前為止我們接觸了不少單表的查詢語句,現在我們來使用連線查詢獲取多個表的資料。

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

下面是各種型別的連線查詢程式碼:

--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%'