How to write queriestring inside the xml file and how to replace the value of a string in the querystring

Question

Hi All,
I have a function call in file1.aspx.cs where I am passing two string values as below.
string strQuery = GlobalQuery.GetQuery(seccondSelection, prefixText);
and inside the GlobalQuery class I have the following code for the static function GetQuery.
public static string GetQuery(string strType, string strLikeChar)
{
  strAT = "sample 1";
  strMK = "sample 2";
  strSN = "sample 3";
 
  string strReturn = string.Empty;
  string strDynamic = string.Empty;
  strDynamic = "Dynamic";
  if ((strLikeChar != "") && (strType != "Aircraft")) strDynamic = strType + "_" + strDynamic;
  else strDynamic = strType;
  dynamicString = strLikeChar.ToUpper(); //first change
  switch (strDynamic)
 {
  case "Aircraft_Dynamic":
  strReturn = "SELECT  h.FUNCTION_NO, Eng_Function_API.Get_Description(FUNCTION_NO) Func_desc "
  + " FROM test_table h "
  + "FROM test_table h  WHERE h.PRODUCT_NO = '" + strAT + "'"
  + " AND h.MODEL_NO = '" + strMK + "'"
  + " UPPER(Eng_Function_API.Get_Description(FUNCTION_NO)) LIKE '" + dynamicString + "%'"
  + " and h.parent_function_no is null ";
  break;
  case "Aircraft":
  strReturn = "SELECT  h.FUNCTION_NO,Eng_Function_API.Get_Description(FUNCTION_NO) Func_desc "
  + "FROM test_table h  WHERE h.PRODUCT_NO = '" + strAT + "'"
  + " AND h.MODEL_NO = '" + strMK + "'"
  + " and h.parent_function_no is null ";
  break;
 // have 2 more case values which will retrieve different set of data.
 } 
}
Now I want know how to write the query part (highlited in red) in XMlL file and how to replace string values inside the query in XML file(highlited in blue)..
I also want to know how to get that querystring from the XML file
string strQuery = GlobalQuery.GetQuery(seccondSelection, prefixText); // GlobalQuery.GetQuery(seccondSelection, prefixText); should be replaced by the XML file which should contain the query part.
Thanks,  Sachi