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我在将行 ID 设置为 TINYINT 数据类型的查找表中插入值时出现算术溢出错误。这不是唯一记录数超过 255 个值的情况。这有点不寻常，并且在此设置的第一次测试期间没有发生。

下面代码的生产版本实际上只有 66 个唯一值，但随着时间的推移，可能会添加新值（缓慢且数量非常少）...... 255 个可用插槽对于这个生命周期来说应该绰绰有余分析过程。

我最初的想法是，这可能是由于缓存计划识别分层源表具有超过 255 个值（实际上有 1028 个），并评估这可能超出目标表的容量。然而，我已经测试过这是不正确的。

-- 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

这似乎不是查询计划缓存问题 - 如果这是真的，我应该会看到方法 1 重新测试的算术错误。

-- 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 中测试了所有 100 个唯一值......因此可以想象，查询代理在第二次插入尝试后看到了 200 条记录的潜力；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，所以最多可能有 200 个唯一值。

有人可以解释一下吗？

4

1 回答 1

0

使用 IGNORE_DUP_KEY 的事件序列是：

  1. 记录已准备好插入，包括 IDENTITY 值的消耗。这使得 IDENTITY 序列上升到 200
  2. 记录被插入。观察到 IGNORE_DUP_KEY 并且插入失败

现在，您失败的一批 INSERT 实际上会生成 IDENTITY 值 201-300，超过 255 的任何值都会溢出您的tinyint列。

通过运行可以轻松验证这一点

select ident_current('tmp_ID10T_Test')

自由地贯穿你的代码。因此，对于您的代码，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
于 2013-04-22T20:47:58.890 回答