如何在 SQL 服务器中将数字转换为 nvarchar？

Question

考虑以下 table。我使用触发器添加到table。在数字转字符串那一栏，失败了

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

你这里有几个问题：

@@IDENTITY 是一个系统函数，包含在 INSERT、SELECT INTO 或 BULK COPY 语句完成。如果该语句不影响任何带有标识列的 table，则 @@IDENTITY returns NULL。如果插入多行，生成多个标识值，@@IDENTITY returns最后生成的标识值。

在你的例子中，你有一个 INSTEAD OF INSERT 触发器，所以没有 INSERT.

下面的查询是完全错误的，会给出错误的结果，只有插入一行时它才能按预期工作，如果多于 1 行，那么这些变量将只保存一行的值，你将丢失其他行的其他值，导致伪 INSERTED 可能包含 1 个或多个行

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

现在，查看您的 table，您已经有一个 IDENTITY 列，所以您根本不需要 TRIGGER，您可以只创建一个计算列作为

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 "a computed column can no longer be selected as the PK. I want this column to be placed in other relevant tables as a FK.I wrote the trigger to get the column value instead of the computed column so that I can select the column as the primary key"。您正在尝试将其设为 PRIMARY KEY，这样您就可以像

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;

See how it's working.

另请参阅这篇文章 Properly Persisted Computed Columns by Paul White。

Answer 2

试试这个

SELECT CONVERT(NVARCHAR(255), @AgentCode)

Answer 3

SELECT CAST([PictureId] AS NVARCHAR(4)) From Category

如何在 SQL 服务器中将数字转换为 nvarchar？

How to convert numeric to nvarchar in SQL Server?

sql

tsql

sql-server

triggers

calculated-columns