SQL算術溢出的標識插入

Question

我有算術溢出值插入一個查找表的行-ID設置爲TINYINT數據類型的錯誤。這不是唯一記錄數超過255個值的情況。這是比較不尋常的，並且在該設置的第一次測試中沒有發生。

量產版下面卻只有66個唯一值的代碼，但它可能是新的值可以加入（緩慢，非常小的數字），隨着時間的推移... 255可用插槽應該是綽綽有餘這個分析過程的壽命。

我最初的想法是，它可能是由於識別分層源表超過255個值（事實上有1028個）的緩存計劃，並且評估這可能會超出目標表的容量。我已經測試過，但這不是真的。

-- This table represents a small (tinyint) subset of unique primary values. 
CREATE TABLE #tmp_ID10T_Test (
ID10T_Test_ID tinyint identity (1,1) not null, 
ID10T_String varchar(255) not null 
PRIMARY KEY CLUSTERED 
(ID10T_String ASC) 
WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = ON, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) 
) ON [PRIMARY] 



-- This table represents a larger (smallint) set of non-unique source values, defined by a secondary key value (Value_Set). 
CREATE TABLE #tmp_ID10T_Values (
ID10T_Value_ID smallint identity (1,1) not null, 
ID10T_Value_Set tinyint not null, 
ID10T_String varchar(255) not null 
) ON [PRIMARY] 



-- Create the initial dataset - 100 unique records; The insertion tests below illustrate that the INDEX is working 
-- correctly on the primary key field for repetative values, however something is happening with the IDENTITY field... 
DECLARE @ID10T tinyint 
, @i tinyint -- A randomized value to determine which subset of printable ASCII characters will be used for the string. 
, @String varchar(255) 

SET @ID10T = 0 
WHILE @ID10T < 100 
    BEGIN 

    SET @String = '' 
     WHILE LEN(@String) < (1+ROUND((254 * RAND(CHECKSUM(NEWID()))),0)) 
     BEGIN 
      SELECT @i = (1 + ROUND((2 * RAND()),0)) -- Randomize which printable character subset is drawn from. 
      SELECT @String = @String + ISNULL(CASE WHEN @i = 1 THEN char(48 + ROUND(((57-48)* RAND(CHECKSUM(NEWID()))),0)) 
      WHEN @i = 2 THEN char(65 + ROUND(((90-65) * RAND(CHECKSUM(NEWID()))),0)) 
      WHEN @i = 3 THEN char(97 + ROUND(((122-97) * RAND(CHECKSUM(NEWID()))),0)) 
      END,'-') 
     END 

    INSERT INTO #tmp_ID10T_Values (ID10T_Value_Set, ID10T_String) 
    SELECT 1, @String 

    SET @ID10T = @ID10T + 1 

    END 

-- Demonstrate that IGNORE_DUP_KEY = ON works for primary key index on string-field 
SELECT * FROM #tmp_ID10T_Values 


-- Method 1 - Simple INSERT INTO: Expect Approx. (100 row(s) affected) 
INSERT INTO #tmp_ID10T_Test (ID10T_String) 
SELECT DISTINCT ID10T_String 
FROM #tmp_ID10T_Values 
GO 


-- Method 2 - LEFT OUTER JOIN WHERE NULL to prevent dupes. 
-- this is the test case to determine whether the procedure cache is mixing plans 
INSERT INTO #tmp_ID10T_Test (ID10T_String) 
SELECT DISTINCT T1.ID10T_String 
FROM #tmp_ID10T_Values AS T1 
LEFT OUTER JOIN #tmp_ID10T_Test AS t2 
ON T1.ID10T_String = T2.ID10T_String 
WHERE T2.ID10T_Test_ID IS NULL 
GO 


-- Repeat Method 1: Duplicate key was ignored (0 row(s) affected). 
INSERT INTO #tmp_ID10T_Test (ID10T_String) 
SELECT DISTINCT ID10T_String 
FROM #tmp_ID10T_Values 
GO 

這似乎不是一個查詢計劃緩存問題 - 我應該看到方法1的算術錯誤重新測試，如果這是真的。

-- Repeat Method 1: Expected: Arithmetic overflow error converting IDENTITY to data type tinyint. 
INSERT INTO #tmp_ID10T_Test (ID10T_String) 
SELECT DISTINCT ID10T_String 
FROM #tmp_ID10T_Values 
GO 

我特別好奇爲什麼會拋出異常。我可以理解，在方法1中，所有100個唯一值都經過測試......因此，可以想象，查詢代理在第二次插入嘗試後會看到200條記錄的潛在可能;我不明白爲什麼它會在第三次重複後看到300條記錄的潛力 - 第二次嘗試導致0行，因此最多可能有200個獨特值。

有人可以解釋這個嗎？

Answer 1

使用IGNORE_DUP_KEY的事件的序列是：

1. 記錄被用於插入件製備，包括標識值的消耗。這使得IDENTITY序列上升到200
2. 記錄被插入。 IGNORE_DUP_KEY觀察和插入被默默失敗

現在你的失敗批插入的實際產生的標識值201-300，爲此，任何超過255溢出的tinyint列。

這是平凡運行

select ident_current('tmp_ID10T_Test') 

寬鬆整個代碼驗證。因此，對於你的代碼，有註釋如下：

-- Method 1 - Simple INSERT INTO: Expect Approx. (100 row(s) affected) 
    -- ident_current = 1 

-- Method 2 - LEFT OUTER JOIN WHERE NULL to prevent dupes. 
    -- ident_current = 100 
    -- NOTE: The SELECT doesn't produce any rows. No rows to insert 

-- Repeat Method 1: Duplicate key was ignored (0 row(s) affected). 
    -- ident_current = 200 
    -- NOTE: SELECT produced 100 rows, which consumed IDENTITY numbers. Later ignored 

-- Repeat Method 1: Expected: Arithmetic overflow error converting IDENTITY to data type tinyint. 
    -- ident_current = 255 
    -- error raised when IDENTITY reaches 256