SQL算术溢出的标识插入

Question

我有算术溢出值插入一个查找表的行-ID设置为TINYINT数据类型的错误。这不是唯一记录数超过255个值的情况。这是比较不寻常的，并且在该设置的第一次测试中没有发生。

量产版下面却只有66个唯一值的代码，但它可能是新的值可以加入（缓慢，非常小的数字），随着时间的推移... 255可用插槽应该是绰绰有余这个分析过程的寿命。

我最初的想法是，它可能是由于识别分层源表超过255个值（事实上有1028个）的缓存计划，并且评估这可能会超出目标表的容量。我已经测试过，但这不是真的。

-- 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 

这似乎不是一个查询计划缓存问题 - 我应该看到方法1的算术错误重新测试，如果这是真的。

-- 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 

我特别好奇为什么会抛出异常。我可以理解，在方法1中，所有100个唯一值都经过测试......因此，可以想象，查询代理在第二次插入尝试后会看到200条记录的潜在可能;我不明白为什么它会在第三次重复后看到300条记录的潜力 - 第二次尝试导致0行，因此最多可能有200个独特值。

有人可以解释这个吗？

Answer 1

使用IGNORE_DUP_KEY的事件的序列是：

1. 记录被用于插入件制备，包括标识值的消耗。这使得IDENTITY序列上升到200
2. 记录被插入。 IGNORE_DUP_KEY观察和插入被默默失败

现在你的失败批插入的实际产生的标识值201-300，为此，任何超过255溢出的tinyint列。

这是平凡运行

select ident_current('tmp_ID10T_Test') 

宽松整个代码验证。因此，对于你的代码，有注释如下：

-- 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