如何根据现有数据进行验证 [英] How to validate against existing data

问题描述

我是个初学者，我给出了用于插入值的编码.现在我想知道如何停止保存现有数据.能否将vb.net中的编码发送给我.(用户不能保存他之前输入的数据)

frens m jus a beginner, i have given the coding for inserting the values. now i want to know how to stop saving the existing data. can u pls send me the coding in vb.net.(user mustn''t be able to save data which he has entered earlier)

推荐答案

在VB级别，您可以轻松地在SQL级别执行以下操作:

In stead of doing at VB level, you can easily perform at SQL level as:

INSERT INTO dbo.Applications (Date, firstname, lastname, Version) VALUES('3/12/2011', 'Tom', 'cruise', '2.0') WHERE NOT EXISTS (SELECT * FROM dbo.Applications WHERE firstname = Tom AND lastname = cruise)

尝试一下.

Try this.

IF((SELECT COUNT(id) FROM Users WHERE username = @username) > 0)
BEGIN
   -- UPDATE STATEMENT
END
ELSE
BEGIN
   -- INSERT STATEMENT
END

问候，
爱德华

Regards,
Eduard

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