C# : My code Doesn't work to prevent repeating barcode value

[Max45]

C# : My code Doesn't work to prevent repeating barcode value
How to fix it ?

    string msg = "";
    try
    {
        //Add Data
        DB.run("insert into item values('" + textBox1.Text.Replace("'", "") + "','" + textBox2.Text.Replace("'", "") + "','" + textBox3.Text.Replace("'", "") + "','" + textBox4.Text.Replace("'", "") + "','" + textBox5.Text.Replace("'", "") + "'," + textBox6.Text.Replace("'", "") + ")");
        msg += "Item Has Been Added Successfully";
        //Add Image
            if (textBox7 != null)
            {
                MemoryStream ms = new MemoryStream();
                pictureBox1.Image.Save(ms, ImageFormat.Jpeg);
                DB.cmd.Parameters.Clear();
                DB.cmd.Parameters.AddWithValue("@img", ms.ToArray());
                DB.run("insert into item_image values(" + textBox1.Text.Replace("'", "") + ",@img)");
                msg += "\n Item's Image Has Been Added Successfully";
                MessageBox.Show(msg);
            if (Application.OpenForms["frmItemSearch"] != null)
                {
                    ((frmItemSearch)Application.OpenForms["frmItemSearch"]).fillData();
                }
            }
        }
    catch (SqlException ex)
    {
        if (ex.Number == 2627)
            MessageBox.Show("Barcode Can Not Be Duplicated.");
        else
            MessageBox.Show(ex.Message);
    }
    }
}

CREATE TABLE [dbo].[item] (
    [item_number]      INT            NOT NULL,
    [item_name]        VARCHAR (250)  NULL,
    [minimum_quantity] NUMERIC (9, 2) NULL,
    [buy_price]        NUMERIC (9, 2) NULL,
    [sale_price]       NUMERIC (9, 2) NULL,
    [barcode]          VARCHAR (60)   NOT NULL,
    CONSTRAINT [PK_item] PRIMARY KEY CLUSTERED ([barcode] ASC, [item_number] ASC),
    UNIQUE NONCLUSTERED ([item_number] ASC)
);

[jmcilhinney]

First of all, stop using string concatenation to insert values into SQL code. You obviously know how to use parameters because you're doing it to save an image, so do it everywhere.

[jmcilhinney]

As for your issue, there is no unique constraint on the barcode. You have only required the combination of barcode and item_number to be unique, not barcode on its own.

[Max45]

As for your issue, there is no unique constraint on the barcode. You have only required the combination of barcode and item_number to be unique, not barcode on its own.

CREATE TABLE [dbo].[item] (
[item_number] INT NOT NULL PRIMARY KEY,
[item_name] VARCHAR (250) NULL,
[minimum_quantity] NUMERIC (9, 2) NULL,
[buy_price] NUMERIC (9, 2) NULL,
[sale_price] NUMERIC (9, 2) NULL,
[barcode] VARCHAR (60) NOT NULL UNIQUE
);