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SQL Server 開窗函數(shù) Over()代替游標(biāo)的使用詳解

前言：

今天在優(yōu)化工作中遇到的sql慢的問題，發(fā)現(xiàn)以前用了挺多游標(biāo)來處理數(shù)據(jù)，這樣就導(dǎo)致在數(shù)據(jù)量多的情況下，需要一行一行去遍歷從而計(jì)算需要的數(shù)據(jù)，這樣處理的結(jié)果就是數(shù)據(jù)慢，容易卡死。

語法介紹：

1、與Row_Number() 函數(shù)結(jié)合使用，對(duì)結(jié)果進(jìn)行排序，這個(gè)是我們使用的非常多的

2、與聚合函數(shù)結(jié)合使用，利用over子句的分組和排序，對(duì)需要的數(shù)據(jù)進(jìn)行操作

例如：SUM() Over() 累加值、AVG() Over() 平均數(shù)
MAX() Over() 最大值、MIN() Over() 最小值

具體介紹：

下面模擬工作中通過開窗函數(shù)代替游標(biāo)的例子，通過期初余額與單據(jù)的預(yù)收金額、應(yīng)收金額、實(shí)收金額來計(jì)算截止本單的期末余額，在以往就是通過游標(biāo)一行一行去遍歷，計(jì)算需要的期末余額，現(xiàn)在使用SUM() Over()來代替，最終要實(shí)現(xiàn)的效果圖如下：

第一行表示標(biāo)題；第二行表示客戶，是一行空行；第三行是期初余額，只顯示期末余額的數(shù)據(jù)，第四至第六行表示的是每種單據(jù)的余額情況，并逐步匯總當(dāng)前行的期末余額數(shù)據(jù)；最后一行表示的是對(duì)客戶的合計(jì)。

1、構(gòu)建需要用到的表和數(shù)據(jù)（簡(jiǎn)略版）

--客戶表
CREATE TABLE Organization(
 FItemID  INT NOT NULL PRIMARY KEY IDENTITY(1,1),
 FNumber  NVARCHAR(255),
 FName  NVARCHAR(255)
)
 
--期初數(shù)據(jù)表
CREATE TABLE InitialData(
 FID   INT NOT NULL PRIMARY KEY IDENTITY(1,1),
 FCustId   INT NOT NULL,
 FPreAmount  DECIMAL(28,10) NOT NULL DEFAULT(0),  --預(yù)收金額
 FReceivableAmount DECIMAL(28,10) NOT NULL DEFAULT(0),  --應(yīng)收金額
 FReceiveAmount  DECIMAL(28,10) NOT NULL DEFAULT(0)  --實(shí)收金額
)
 
--單據(jù)明細(xì)表
CREATE TABLE DetailData(
 FID   INT NOT NULL PRIMARY KEY IDENTITY(1,1),
 FCustId   INT NOT NULL,
 FDate   DATETIME NOT NULL,
 FBillType  NVARCHAR(64) NOT NULL,
 FBillNo   NVARCHAR(64) NOT NULL,
 FPreAmount  DECIMAL(28,10) NOT NULL DEFAULT(0),  --預(yù)收金額
 FReceivableAmount DECIMAL(28,10) NOT NULL DEFAULT(0),  --應(yīng)收金額
 FReceiveAmount  DECIMAL(28,10) NOT NULL DEFAULT(0)  --實(shí)收金額
)
 
INSERT INTO Organization(FNumber,FName) VALUES('001','北京客戶')
INSERT INTO Organization(FNumber,FName) VALUES('002','上海客戶')
INSERT INTO Organization(FNumber,FName) VALUES('003','廣州客戶')
 
INSERT INTO InitialData(FCustId,FPreAmount,FReceivableAmount,FReceiveAmount)
VALUES(1,0,0,0)
INSERT INTO InitialData(FCustId,FPreAmount,FReceivableAmount,FReceiveAmount)
VALUES(2,8000,7245,0)
INSERT INTO InitialData(FCustId,FPreAmount,FReceivableAmount,FReceiveAmount)
VALUES(3,0,1068.21,1068.00)
 
INSERT INTO DetailData(FCustId,FDate,FBillType,FBillNo,FPreAmount,FReceivableAmount,FReceiveAmount)
VALUES(1,'2020-06-30','委托結(jié)算','XSD20200700008',0,1221.56,0)
INSERT INTO DetailData(FCustId,FDate,FBillType,FBillNo,FPreAmount,FReceivableAmount,FReceiveAmount)
VALUES(1,'2020-06-30','委托結(jié)算','XSD20200700009',0,373.46,0)
INSERT INTO DetailData(FCustId,FDate,FBillType,FBillNo,FPreAmount,FReceivableAmount,FReceiveAmount)
VALUES(1,'2020-06-30','委托結(jié)算退貨','XSD20200700010',0,-427.05,0)
INSERT INTO DetailData(FCustId,FDate,FBillType,FBillNo,FPreAmount,FReceivableAmount,FReceiveAmount)
VALUES(1,'2020-07-30','銷售商品返利','XSFL20200700005',0,-17.9,0)
 
INSERT INTO DetailData(FCustId,FDate,FBillType,FBillNo,FPreAmount,FReceivableAmount,FReceiveAmount)
VALUES(2,'2020-06-25','預(yù)收退款','SKD20200700002',-755,0,0)
INSERT INTO DetailData(FCustId,FDate,FBillType,FBillNo,FPreAmount,FReceivableAmount,FReceiveAmount)
VALUES(2,'2020-06-20','銷售發(fā)貨','XSD20200700006',0,6169.50,6169.50)
INSERT INTO DetailData(FCustId,FDate,FBillType,FBillNo,FPreAmount,FReceivableAmount,FReceiveAmount)
VALUES(2,'2020-07-30','銷售總額返利','XSFL20200700002',0,-493.56,-421.85)
INSERT INTO DetailData(FCustId,FDate,FBillType,FBillNo,FPreAmount,FReceivableAmount,FReceiveAmount)
VALUES(2,'2020-07-31','其他應(yīng)收','QTYS20200900001',0,6000.00,0)
INSERT INTO DetailData(FCustId,FDate,FBillType,FBillNo,FPreAmount,FReceivableAmount,FReceiveAmount)
VALUES(2,'2020-06-20','預(yù)收沖應(yīng)收','HXD20200700006',-7245.00,0,7245.00)
 
INSERT INTO DetailData(FCustId,FDate,FBillType,FBillNo,FPreAmount,FReceivableAmount,FReceiveAmount)
VALUES(3,'2020-06-30','銷售收款','SKD20200700003',0,0,2386.96)
INSERT INTO DetailData(FCustId,FDate,FBillType,FBillNo,FPreAmount,FReceivableAmount,FReceiveAmount)
VALUES(3,'2020-06-30','應(yīng)收轉(zhuǎn)應(yīng)收','HXD20200700007',0,2386.75,0)
INSERT INTO DetailData(FCustId,FDate,FBillType,FBillNo,FPreAmount,FReceivableAmount,FReceiveAmount)
VALUES(3,'2020-07-08','銷售退貨','XSD20200700014',0,-46.80,0)
GO

2、以往的游標(biāo)寫法

SET NOCOUNT ON
--建立臨時(shí)表處理獲取數(shù)據(jù)
CREATE TABLE #DATA(
 FID   INT NOT NULL PRIMARY KEY IDENTITY(1,1),
 FClassTypeId  INT NOT NULL,
 FCustId   INT NOT NULL,
 FNumber   NVARCHAR(255),
 FName   NVARCHAR(255),
 FDate   DATETIME NULL,
 FBillType  NVARCHAR(64) NULL,
 FBillNo   NVARCHAR(64) NULL,
 FPreAmount  DECIMAL(28,10) NOT NULL DEFAULT(0),  --預(yù)收金額
 FReceivableAmount DECIMAL(28,10) NOT NULL DEFAULT(0),  --應(yīng)收金額
 FReceiveAmount  DECIMAL(28,10) NOT NULL DEFAULT(0),  --實(shí)收金額
 FBalanceAmount  DECIMAL(28,10) NOT NULL DEFAULT(0)    --期末余額
)
 
Declare @Id     INT
Declare @CustId    INT
Declare @PreAmount   decimal(28,10)
Declare @ReceivableAmount decimal(28,10)
Declare @ReceiveAmount  decimal(28,10)
Declare @OldCustId   int
Declare @Count    int
Declare @LastAmount   decimal(28,10)
Declare @SumPreAmount  decimal(28,10)
Declare @SumReceivableAmount decimal(28,10)
Declare @SumReceiveAmount decimal(28,10)
Declare @SumBalanceAmount decimal(28,10)
 
--使用游標(biāo)
Declare Data_cursor Cursor
For Select FID,FCustId,FPreAmount,FReceivableAmount,FReceiveAmount
 From DetailData
 Order By FCustId,FDate,FID
OPEN Data_cursor
FETCH NEXT FROM Data_Cursor INTO @Id,@CustId,@PreAmount,@ReceivableAmount,@ReceiveAmount
SET @OldCustId = @CustId
SET @Count = 0
SET @LastAmount = 0
SET @SumPreAmount = 0
SET @SumReceivableAmount = 0
SET @SumReceiveAmount = 0
SET @SumBalanceAmount = 0
WHILE @@FETCH_STATUS = 0
BEGIN 
 IF @Count > 0
 BEGIN
  IF @OldCustId > @CustId 
  BEGIN
   --表示客戶已經(jīng)變了，要插入小計(jì)
   SET @Count = 0
   INSERT INTO #DATA(FClassTypeId,FBillType,FCustId,FNumber,FName,FPreAmount,FReceivableAmount,FReceiveAmount,FBalanceAmount)
   SELECT -9999,FName + '小計(jì)',FItemID,FNumber,FName,@SumPreAmount,@SumReceivableAmount,@SumReceiveAmount,@LastAmount
   FROM Organization
   WHERE FItemID = @OldCustId
   Select @SumPreAmount=0,@SumReceivableAmount=0,@SumReceiveAmount=0,@SumBalanceAmount=0,@LastAmount=0
  END  
 END 
 IF @Count = 0
 BEGIN
  Set @OldCustId=@CustId
  --插入一行空行
  INSERT INTO #DATA(FClassTypeId,FBillType,FCustId,FNumber,FName)
  SELECT -1000,FName,FItemID,FNumber,FName
  FROM Organization
  WHERE FItemID = @CustId
 
  --獲取期初的期末余額
  SELECT @LastAmount=isnull(FReceivableAmount,0) - isnull(FPreAmount,0) - isnull(FReceiveAmount,0),@PreAmount=isnull(FPreAmount,0),@ReceivableAmount=isnull(FReceivableAmount,0),@ReceiveAmount=isnull(FReceiveAmount,0)
  FROM InitialData
  WHERE FCustId = @CustId
 
  INSERT INTO #DATA(FClassTypeId,FBillType,FCustId,FNumber,FName,FBalanceAmount)
  VALUES(-1000,'期初余額',@CustId,'','',@LastAmount)
 
  SELECT @Count = 1
  SELECT @SumBalanceAmount = @LastAmount
 END 
 
 --插入單據(jù)明細(xì)
 INSERT INTO #DATA(FClassTypeId,FCustId,FNumber,FName,FDate,FBillType,FBillNo,FPreAmount,FReceivableAmount,FReceiveAmount,FBalanceAmount)
 SELECT 0,d.FCustId,o.FNumber,o.FName,FDate,FBillType,FBillNo,FPreAmount,FReceivableAmount,FReceiveAmount,@LastAmount + FReceivableAmount - FPreAmount - FReceiveAmount
 FROM DetailData d
 INNER JOIN Organization o ON d.FCustId = o.FItemID
 WHERE d.FCustId = @CustId AND FID = @Id
 
 SELECT
 @LastAmount = @LastAmount + FReceivableAmount - FPreAmount - FReceiveAmount,
 @SumPreAmount=@SumPreAmount + FPreAmount,@SumReceivableAmount=@SumReceivableAmount + FReceivableAmount,
 @SumReceiveAmount=@SumReceiveAmount + FReceiveAmount
 FROM DetailData
 WHERE FCustId = @CustId AND FID = @Id
 
 FETCH NEXT FROM Data_cursor INTO @Id,@CustId,@PreAmount,@ReceivableAmount,@ReceiveAmount
END
IF @Count > 0
BEGIN
 INSERT INTO #DATA(FClassTypeId,FBillType,FCustId,FNumber,FName,FPreAmount,FReceivableAmount,FReceiveAmount,FBalanceAmount)
 SELECT -9999,FName + '小計(jì)',FItemID,FNumber,FName,@SumPreAmount,@SumReceivableAmount,@SumReceiveAmount,@LastAmount
 FROM Organization
 WHERE FItemID = @OldCustId
 Select @SumPreAmount=0,@SumReceivableAmount=0,@SumReceiveAmount=0,@SumBalanceAmount=0,@LastAmount=0
END
CLOSE Data_cursor
DEALLOCATE Data_cursor
 
SELECT * FROM #DATA
ORDER BY FCustId,FID
 
DROP TABLE #DATA

代碼說明：創(chuàng)建了一個(gè)臨時(shí)表，使用游標(biāo)遍歷我們的DetailData數(shù)據(jù)表，為了呈現(xiàn)我們最終需要的數(shù)據(jù)樣式，插入客戶空行、期初余額、單據(jù)信息、客戶小計(jì)等，逐行計(jì)算期末余額值的情況，最終效果如下：

3、使用SUM() Over()的寫法

SET NOCOUNT ON
--建立臨時(shí)表處理獲取數(shù)據(jù)
CREATE TABLE #DATA(
 FID     INT NOT NULL PRIMARY KEY IDENTITY(1,1),
 FClassTypeId  INT NOT NULL,
 FCustId    INT NOT NULL,
 FNumber    NVARCHAR(255),
 FName    NVARCHAR(255),
 FDate    DATETIME NULL,
 FBillType   NVARCHAR(64) NULL,
 FBillNo    NVARCHAR(64) NULL,
 FPreAmount   DECIMAL(28,10) NOT NULL DEFAULT(0),  --預(yù)收金額
 FReceivableAmount DECIMAL(28,10) NOT NULL DEFAULT(0),  --應(yīng)收金額
 FReceiveAmount  DECIMAL(28,10) NOT NULL DEFAULT(0),  --實(shí)收金額
 FBalanceAmount  DECIMAL(28,10) NOT NULL DEFAULT(0)  --期末余額
)
 
--插入空行
INSERT INTO #DATA(FClassTypeId,FBillType,FCustId,FNumber,FName)
SELECT -1000,FName,FItemID,FNumber,FName
FROM Organization o
INNER JOIN (SELECT FCustId FROM DetailData GROUP BY FCustId) d ON d.FCustId = o.FItemID
 
--插入期初余額
INSERT INTO #DATA(FClassTypeId,FBillType,FCustId,FNumber,FName,FBalanceAmount)
SELECT -1000,'期初余額',FItemID,'','',i.FReceivableAmount - i.FPreAmount -i.FReceiveAmount
FROM Organization o
INNER JOIN InitialData i ON o.FItemID = i.FCustId
INNER JOIN (SELECT FCustId FROM DetailData GROUP BY FCustId) d ON d.FCustId = o.FItemID
 
--插入單據(jù)明細(xì)(關(guān)鍵代碼SUM() Over() )
INSERT INTO #DATA(FClassTypeId,FCustId,FNumber,FName,FDate,FBillType,FBillNo,FPreAmount,FReceivableAmount,FReceiveAmount,FBalanceAmount)
SELECT 0,d.FCustId,o.FNumber,o.FName,d.FDate,d.FBillType,d.FBillNo,d.FPreAmount,d.FReceivableAmount,d.FReceiveAmount,
SUM(d.FReceivableAmount - d.FPreAmount - d.FReceiveAmount) OVER(PARTITION BY d.FCustId ORDER BY d.FCustId,d.FDate,d.FID)
+ i.FReceivableAmount - i.FPreAmount - i.FReceiveAmount
FROM DetailData d WITH(NOLOCK)
INNER JOIN Organization o WITH(NOLOCK) ON o.FItemID = d.FCustId
INNER JOIN InitialData i WITH(NOLOCK) ON o.FItemID = i.FCustId
ORDER BY d.FCustId,d.FDate,d.FID
 
--插入小計(jì)
INSERT INTO #DATA(FClassTypeId,FBillType,FCustId,FNumber,FName,FPreAmount,FReceivableAmount,FReceiveAmount,FBalanceAmount)
SELECT -9999,FName + '小計(jì)',d.FCustId,FNumber,FName,SUM(FPreAmount),SUM(FReceivableAmount),SUM(FReceiveAmount),0
FROM dbo.DetailData d
INNER JOIN dbo.Organization o ON d.FCustId = o.FItemID
GROUP BY d.FCustId,o.FName,o.FNumber
 
--更新小計(jì)的期末余額
UPDATE d SET d.FBalanceAmount = d.FReceivableAmount - d.FPreAmount - d.FReceiveAmount + i.FReceivableAmount - i.FPreAmount - i.FReceiveAmount
FROM #DATA d
INNER JOIN InitialData i ON d.FCustId = i.FCustId
WHERE d.FClassTypeId = -9999
 
SELECT * FROM #DATA
ORDER BY FCustId,FID
 
DROP TABLE #DATA

代碼說明：相比第二種，去除了游標(biāo)的寫法，通過了

SUM(d.FReceivableAmount - d.FPreAmount - d.FReceiveAmount) OVER(PARTITION BY d.FCustId ORDER BY d.FCustId,d.FDate,d.FID)

來計(jì)算我們需要的值，這個(gè)語法說明一下，sum是累加計(jì)算，計(jì)算應(yīng)收金額 - 預(yù)收金額 - 實(shí)收金額（第二行計(jì)算出來的結(jié)果要加上第一行計(jì)算出來的結(jié)果，第三行計(jì)算出來的結(jié)果要加上第二行計(jì)算出來的結(jié)果，依次類推，所以，其他聚合函數(shù)也是這種用法哦），PARTITION BY分組統(tǒng)計(jì)客戶，并通過Order by指定排序
這個(gè)PARTITION BY和Order By結(jié)果的用法就很關(guān)鍵了，不然計(jì)算就不是預(yù)期想要的
再舉個(gè)例子：比如使用Count() Over() 計(jì)算客戶的訂單號(hào)

SELECT DISTINCT FCustId,COUNT(FBillNo) OVER(PARTITION BY FCustId) FBillNum FROM DetailData

總結(jié)：

1、游標(biāo)的使用場(chǎng)景可以很廣，但是在數(shù)據(jù)量大的時(shí)候，就會(huì)顯得很慢，一行一行遍歷的速度還是挺久的

2、使用開窗函數(shù)來實(shí)現(xiàn)一些功能，還是很方便能實(shí)現(xiàn)效果，并且它的速度也是很快，值得推薦。

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