[英]How to convert numeric to nvarchar in SQL Server?
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
你在这里有几个问题:
@@IDENTITY
是一个系统函数,包含在INSERT
、 SELECT INTO
或BULK COPY
语句完成时生成的最后一个标识值。 如果该语句不影响具有标识列的任何表, @@IDENTITY
返回NULL
。 如果插入多行,生成多个标识值, @@IDENTITY
返回生成的最后一个标识值。
在您的情况下,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,会给出错误的结果,只有在插入一行时它才能按预期工作,如果有超过 1 行,那么这些变量将只保存一行的值,而您将丢失其他值其他行,导致伪INSERTED
可能包含 1 行或更多行
select @AgentCode=AgentCode,
@NationalCode=NationalCode,
@FirstName=FirstName,
@LastName=LastName,
@IsActive=IsActive
from inserted
现在,查看您的表,您已经有一个IDENTITY
列,因此您根本不需要TRIGGER
,您只需创建一个计算列即可
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“无法再选择计算列作为 PK。我希望将此列作为 FK 放置在其他相关表中。我编写了触发器来获取列值而不是计算列,以便我可以选择该列作为主键" 。 您正在尝试将其设为PRIMARY KEY
以便您可以这样做
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;
另请参阅Paul White
撰写的这篇文章Properly Persisted Computed Columns
。
尝试这个
SELECT CONVERT(NVARCHAR(255), @AgentCode)
SELECT CAST([PictureId] AS NVARCHAR(4)) From Category
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