返回SQL语句的问题

C# code

try        {            try            {                brand = Request.QueryString["brand"].Trim();                price = Request.QueryString["price"].Trim();                graphics = Request.QueryString["graphics"].Trim();                size = Request.QueryString["size"].Trim();            }            catch (Exception exone)            {                            }            DataConn Conn = new DataConn();            if (brand == "" && price == "" && size == "" && graphics == "")            {                sql = "select * from TB_Laptop";                Response.Write("<script>alert('!!!')</script>");            }            else            {                Response.Write("<script>alert('!!!')</script>");                try                {                    sql = "select * from TB_Laptop where Type='laptop'";                    if (brand != "")                        sql += " and SearchBrand='" + brand + "'"; //从这里开始后面的就不执行了。。                      Response.Write("<script>alert('1" + sql + "')</script>");                    if (price != "")                        sql += " and SearchPrice='" + price + "'";                    Response.Write("<script>alert('2" + sql + "')</script>");                    if (size != "")                        sql += " and SearchSize='" + size + "'";                    Response.Write("<script>alert('3" + sql + "')</script>");                    if (graphics != "")                        sql += " and SearchGraphics='" + graphics + "'";                    Response.Write("<script>alert('4" + sql + "')</script>");                }                catch (Exception extwo) {                    Response.Write("<script>alert('" + extwo.Message + "')</script>");                }            }            Response.Write("<script>alert('!!!')</script>");            Conn.ExcuteSearch(sql);            DT = new DataTable();            DT = Conn.MyDT;            if (DT.Rows.Count < 1)            {                Response.Write("<script>alert('抱歉，我们暂时还未收录您所筛选的商品！感谢您对我们的支持！')</script>");            }            else            {                DataList1.DataSource = DT;                DataList1.DataBind();            }        }        catch (Exception ex) {            Response.Write("<script>alert('"+ex.Message+"')</script>");        }

问题 我的SQL+=操作有问题？
正确的写法是啥？

[解决办法]
如果没有特殊字符，数据类型匹配，没有问题。
你可以Response.Write(sql)看是否是合法的sql语句
[解决办法]
设个断点调试一下，看看各变量的值，找出原因。
[解决办法]

探讨

直接赋值就是对的。。。
还是
sql = "select * from TB_Laptop where Type='laptop'";
if (brand != "")
sql += " and SearchBrand='" + brand + "'"; //从这里开始后面的就不执行了。。 ……

[解决办法]
SearchPrice字段的数据类型是否是varchar?如不是，应该去掉引号，即：

sql += " and SearchPrice=" + price;

其他字段的数据类型也检查一下

------解决方案--------------------

if (brand != "")
sql += " and SearchBrand='" + brand + "'"; //从这里开始后面的就不执行了。。
LZ 你在这里断点测试一下，看看brand的值