Check if A CONSTRAINT UNIQUE already exists in a table? Visual Basic .NET Access

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Check if A CONSTRAINT UNIQUE already exists in a table? Visual Basic .NET Access

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I'm in Visual Basic trying to make a program to manage a database, well I have the following SQL statement in the program to add UNIQUE to two fields of a table:

"ALTER TABLE RESEARCHERS ADD CONSTRAINT RESEARCHERS UNIQUE (resEmail, 
resPhoneNumber);"

But I want to make sure that before adding it, check if it already exists, since otherwise the program gives an error.

sql vb.net ms-access

asked by Pedro López 27.04.2017 в 13:59

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score 0 · Answer 1

You need to make a prior consultation, or make the attempt of INSERT (which I assume is what you want to do) and check if there is an error:

Try
    ; Tu instrucción a la BD (ExecuteNonQuery())
Catch ex As SqlException
    MessageBox.Show(ex.Message, _
        "Error en la base de datos", _
        MessageBoxButtons.OK, _
        MessageBoxIcon.Exclamation,
End Try

I recommend this because you avoid an additional query to the database in case everything is fine, and if an error happens you can easily inform the user about it.