如何在SQL Server中将数字转换为nvarchar？

Question

请考虑下表。我使用触发器添加到表中。在将数字转换为字符串的列中，它失败。

CREATE TABLE [dbo].[tblAIAgent]
(
    [AgentCode] [NVARCHAR](10) NOT NULL,
    [NationalCode] [BIGINT] NOT NULL 
         CONSTRAINT [DF_tblAIAgent_NationalCode]  DEFAULT ((0)),
    [FirstName] [NVARCHAR](50) NOT NULL 
         CONSTRAINT [DF_tblAIAgent_Name] DEFAULT (''),
    [LastName] [NVARCHAR](50) NOT NULL 
         CONSTRAINT [DF_tblAIAgent_Family] DEFAULT (''),
    [IsActive] [BIT] NOT NULL 
         CONSTRAINT [DF_tblAIAgent_Active] DEFAULT ((1)),
    [Counter] [INT] IDENTITY(1,1) NOT NULL,

    CONSTRAINT [PK_tblAIAgent] 
        PRIMARY KEY CLUSTERED 
)

ALTER TRIGGER [dbo].[AgentInsert] 
ON [dbo].[tblAIAgent]
INSTEAD OF INSERT
AS
BEGIN
    DECLARE @AgentCode NVARCHAR(10)
    DECLARE @NationalCode BIGINT
    DECLARE @FirstName NVARCHAR(50)
    DECLARE @LastName NVARCHAR(50)
    DECLARE @IsActive BIT
    DECLARE @CounterIs INT

    SET @CounterIs = @@IDENTITY

    SELECT
        @AgentCode = AgentCode,
        @NationalCode = NationalCode,
        @FirstName = FirstName,
        @LastName = LastName,
        @IsActive = IsActive 
    FROM inserted

    INSERT INTO tblAIAgent (NationalCode, FirstName, LastName, IsActive, AgentCode)
    VALUES (@NationalCode, @FirstName, @LastName, @IsActive, 'Agent_' + CAST(@CounterIs AS NVARCHAR(4))) 
END

Answer 1

您在这里遇到一些问题：

该@@IDENTITY是一个系统函数包含时所生成的最后一个标识值INSERT，SELECT INTO或BULK COPY完成陈述。如果该语句不影响任何带有标识列的表，则@@IDENTITY返回NULL。如果插入了多行，生成了多个标识值，则@@IDENTITY返回最后生成的标识值。

就您而言，您有一个INSTEAD OF INSERT触发器，因此没有INSERT。

下面的查询是完全错误的，并且将给出错误的结果，仅当插入一行时，它才能按预期工作；如果多于1行，则这些变量将仅保留一行的值，而您将丢失其他值其他行，因为伪INSERTED可能包含1个或更多行

select @AgentCode=AgentCode,
       @NationalCode=NationalCode,
       @FirstName=FirstName,
       @LastName=LastName,
       @IsActive=IsActive 
from inserted

现在，在您的表上查找，您已经有一个IDENTITY列，因此完全不需要TRIGGER，您只需将计算列设为

CREATE TABLE [dbo].[tblAIAgent](
    [AgentCode] AS 'Agent_' + CAST([Counter] AS VARCHAR(10)),
    [NationalCode] [bigint] NOT NULL 
    CONSTRAINT [DF_tblAIAgent_NationalCode]  DEFAULT ((0)),
    [FirstName] [nvarchar](50) NOT NULL 
    CONSTRAINT [DF_tblAIAgent_Name]  DEFAULT (''),
    [LastName] [nvarchar](50) NOT NULL 
    CONSTRAINT [DF_tblAIAgent_Family]  DEFAULT (''),
    [IsActive] [bit] NOT NULL 
    CONSTRAINT [DF_tblAIAgent_Active]  DEFAULT ((1)),
    [Counter] [int] IDENTITY(1,1) NOT NULL,
    CONSTRAINT [PK_tblAIAgent] PRIMARY KEY ([Counter])
    );

更新：

根据您的评论“不能再将计算列选作PK。我希望将此列作为FK放置在其他相关表中。我编写了触发器以获取列值而不是计算列，以便我可以选择该列作为主键”。您正在尝试使其成为一种，PRIMARY KEY因此您可以

CREATE TABLE T(
  Counter INT IDENTITY(1,1) NOT NULL,
  OtherCol INT,
  Computed AS CONCAT('Agent_', CAST(Counter AS VARCHAR(10))) PERSISTED,
  CONSTRAINT PKT PRIMARY KEY(Computed)
);

CREATE TABLE TT(
  ReferenceComputedColumn VARCHAR(16) NOT NULL,
  OtherColumn INT,
  CONSTRAINT FK_ReferencedComputedColumn 
      FOREIGN KEY(ReferenceComputedColumn) 
      REFERENCES T(Computed)
)

INSERT INTO T(OtherCol) VALUES
(1), (2), (3);

INSERT INTO TT(ReferenceComputedColumn, OtherColumn) VALUES
('Agent_1', 10),
('Agent_3', 20);

SELECT *
FROM T LEFT JOIN TT 
ON T.Computed = TT.ReferenceComputedColumn;

看看它是如何工作的。

也看到这篇文章Properly Persisted Computed Columns的Paul White。