15個初學者必看的基礎SQL查詢語句
阿新 • • 發佈：2019-02-19
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
ItemMasters3、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 ItemMasters4、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 ItemmastersDatePart –> 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())) MonthDifferance5、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 DESCSelect * 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 ItemMasters6、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>3Where – 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 DescWhere – 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_CodeGroup 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 ItemMasters9、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%'