ASP.NET查询中的奇怪行为

Question

我试图在后面的代码中构建查询，并将其连接到数据源以重新加载数据。 不幸的是，该查询仅在where子句中包含Author时才有效。 否则，我没有返回任何结果。

例如：

1. 仅搜索作者（国王），即可返回准确的结果。

    SELECT [Title], [Author], [Category], [Image], [Binding], [Price], [ProductID], [Average Rating] AS Average_Rating FROM [tblProducts] WHERE (Author LIKE '%king%') 

2. 搜索作者（国王）和标题（dif），返回准确的结果。

    SELECT [Title], [Author], [Category], [Image], [Binding], [Price], [ProductID], [Average Rating] AS Average_Rating FROM [tblProducts] WHERE (Author LIKE '%king%') AND (Title LIKE '%dif%') 

3. 仅搜索标题（dif），没有返回结果。

    SELECT [Title], [Author], [Category], [Image], [Binding], [Price], [ProductID], [Average Rating] AS Average_Rating FROM [tblProducts] WHERE (Title LIKE '%dif%') 

4. 如果所有用户输入的值均为空，则不会返回任何结果。

    SELECT [Title], [Author], [Category], [Image], [Binding], [Price], [ProductID], [Average Rating] AS Average_Rating FROM [tblProducts] 

我敢肯定，这很简单，但是我无法弄清楚。 任何帮助表示赞赏。

这是我的相关代码：

if (Page.IsValid)
{
    System.Web.UI.WebControls.AccessDataSource tmpAccessConnection = new System.Web.UI.WebControls.AccessDataSource();

    //Set file location
    //Connection strings are not used with unprotected Access databases
    tmpAccessConnection.DataFile = "~/App_Data/propdbA2003.mdb";
    tmpAccessConnection.ID = "adsPropertyListing";
    tmpAccessConnection.DataSourceMode = SqlDataSourceMode.DataSet;

    //build query
    tmpAccessConnection.SelectCommand = "SELECT [Title], [Author], [Category], " +
    "[Image], [Binding], [Price], [ProductID], [Average Rating] AS Average_Rating " +
    " FROM [tblProducts]";

    String stmntWhere = "";

    if (!textAuthor.Text.Equals(""))
    {
        stmntWhere += "(Author LIKE '%" + textAuthor.Text + "%')";
    }

    if (!textBookTitle.Text.Equals(""))
    {
        if(!stmntWhere.Equals(""))
            stmntWhere += " AND "; //add AND if the stmnt has other parameters
        stmntWhere += "(Title LIKE '%" + textBookTitle.Text + "%')";
    }

    if (!textISBN.Text.Equals(""))
    {
        if (!stmntWhere.Equals(""))
            stmntWhere += " AND "; //add AND if the stmnt has other parameters
        stmntWhere += "((ISBN LIKE '%" + textISBN.Text + "%')" + 
                    " OR (ISBN13 LIKE '%" + textISBN.Text + "%'))";
    }

    if (checkInclude.Checked)
    {
        if (!stmntWhere.Equals(""))
           stmntWhere += " AND "; //add AND if the stmnt has other parameters
        stmntWhere += "(Category = " + dropDwnCategory.SelectedValue + ")";
    }

    if (!stmntWhere.Equals(""))
        tmpAccessConnection.SelectCommand += " WHERE " + stmntWhere;

    adsSearch.SelectCommand = tmpAccessConnection.SelectCommand;
    anAccessDataSource.SelectCommand = tmpAccessConnection.SelectCommand;
    gridViewBrowseAll.DataSourceID = "adsSearch";

    //reset page to 1st page if new search is initiated from revised query
    gridViewBrowseAll.PageIndex = 0;

    //Set AutoGenerateColumns property to true in code or web form
    try
    {
        gridViewBrowseAll.DataBind();
    }
    catch (Exception ex)
    {
        Response.Write("Binding exception in btnPropNoSearch_Click<BR>");
        Response.Write("Access Exception Handler: {0} " + ex.ToString());
    }
}