如果记录不存在，则插入表中答案

【问题标题】：Insert into table if record does not already exist如果记录不存在，则插入表中
【发布时间】：2014-03-08 07:40:21
【问题描述】：

由于某种原因，这给了我“无法在表中插入重复记录”的错误。

INSERT  INTO [DMS].[dbo].[Deductions]
        (
         CustomerID,
         DeductionCode,
         DeductionDescription
        )
        SELECT  b.CustomerID,
                b.AdjustmentReason,
                b.AdjustmentReason
        FROM    @CreditDebitAdjustmentDetail b
        WHERE   NOT EXISTS ( SELECT 1
                             FROM   [DMS].[dbo].[Deductions]
                             WHERE  CustomerID = b.CustomerID
                                    AND DeductionCode = b.AdjustmentReason )

奇怪的是，我是这样测试的：

DECLARE @CreditDebitAdjustmentDetail TABLE
        (
         CustomerID INT,
         AdjustmentReason VARCHAR(50)
        )

INSERT  INTO @CreditDebitAdjustmentDetail
        (CustomerID, AdjustmentReason)
VALUES  (143, -- CustomerID - int
         '024'  -- AdjustmentReason - varchar(50)
         )

INSERT  INTO [DMS].[dbo].[Deductions]
        (
         CustomerID,
         DeductionCode,
         DeductionDescription
        )
        SELECT  b.CustomerID,
                b.AdjustmentReason,
                b.AdjustmentReason
        FROM    @CreditDebitAdjustmentDetail b
        WHERE   NOT EXISTS ( SELECT 1
                             FROM   [DMS].[dbo].[Deductions]
                             WHERE  CustomerID = b.CustomerID
                                    AND DeductionCode = b.AdjustmentReason )

并且它不会插入到表中，因为记录已经存在。

我错过了什么吗？

编辑 - 我以为我已经通过这样做修复了它，但我仍然遇到同样的错误：

INSERT  INTO [DMS].[dbo].[Deductions]
        (
         CustomerID,
         DeductionCode,
         DeductionDescription
        )
        SELECT  a.CustomerID,
                a.AdjustmentReason,
                a.AdjustmentReason
        FROM    @CreditDebitAdjustmentDetail a
        WHERE   NOT EXISTS ( SELECT 1
                             FROM   [DMS].[dbo].[Deductions] b
                             WHERE  a.CustomerID = b.CustomerID
                                    AND a.AdjustmentReason = b.DeductionCode )

【问题讨论】：

看看你的索引
也许CustomerId 或DeductionCode 在Deductions 表或用于更新的表中是NULL。允许一个NULL，但不允许多个NULLs。
你的PK中有哪些列？
CustomerID 和 DeductionCode = 在 Deductions 表中唯一。
我想我发现了这个问题。发生 INSERT 时，CustomerID 为 NULL。一旦我弄清楚了，我会报告的。

标签： sql-server tsql not-exists

【解决方案1】：

我想通了，DOH！

关键字 ... DISTINCT -_-

INSERT INTO [DMS].[dbo].[Deductions]
                    (
                     CustomerID,
                     DeductionCode,
                     DeductionDescription
                    )
                    SELECT  DISTINCT
                            a.CustomerID,
                            ISNULL(a.AdjustmentReason, 'UNKNOWN'),
                            ISNULL(a.AdjustmentReason, 'UNKNOWN')
                    FROM    @CreditDebitAdjustmentDetail a
                    WHERE   NOT EXISTS ( SELECT 1
                                         FROM   [DMS].[dbo].[Deductions] b
                                         WHERE  a.CustomerID = b.CustomerID
                                                AND CASE a.AdjustmentReason
                                                      WHEN NULL THEN 'UNKNOWN'
                                                      WHEN '' THEN 'UNKNOWN'
                                                    END = b.DeductionCode )

【讨论】：