c#更新语句出错

string sql = "update text1 set bh='" + textBox1.Text + "',mc='" + textBox2.Text + "',bz='" + textBox3.Text + "'where bh=this.dataGridView1.SelectedRows[0].Cells[0].Value.ToString()";


到底是哪里错了，最后那一段是获取选中行的值（bh=this.dataGridView1.SelectedRows[0].Cells[0].Value.ToString()）应该怎么改成sql语句