[ASP.NET C＃]在gridview中使用过滤器仅显示一条记录

Question

嗨，我有一个问题，就像学期和学校一样搜索2个值，它只给我一条记录，而我找到了至少30条记录。

string conn = ConfigurationManager.ConnectionStrings["MyDatabase"].ConnectionString;
        using (SqlConnection sqlcon = new SqlConnection(conn))
        {
            using (SqlCommand cmd = new SqlCommand())
            {
                cmd.CommandText = "SELECT *FROM tblEvaluation WHERE Semester LIKE '%' + @sem +  '%' and SchoolYear like '%' + @sy +  '%'";
                cmd.Connection = sqlcon;
                cmd.Parameters.AddWithValue("@sem", DropDownList1.Text);
                cmd.Parameters.AddWithValue("@sy", DropDownList2.Text);
                DataTable dt = new DataTable();
                using (SqlDataAdapter sda = new SqlDataAdapter(cmd))
                {
                    sda.Fill(dt);
                    GridView1.DataSource = dt;
                    GridView1.DataBind();
                }
            }
        }