private void button1_Click (object sender, EventArgs e) 
{
If (textBox1. Text=="" | | comboBox1. Text==" ") 
MessageBox. Show (" tip: please enter!" , "warning"); 
The else 
{
If (this.com boBox1. Text=="student id") 
{
String STR=@ "Data Source=lenovo - PC \ sqlexpress; Initial catalog=users; Integrated Security=True "; 
SqlConnection conn=new SqlConnection (STR); 
conn.Open(); 
String SQL="Delete from performance information where student id='" + textBox1. Text +"' "; 
SqlCommand CMD=new SqlCommand (SQL, conn); 
conn.Close(); 
} 
} 
}

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