Building a query through asp.net controls value selection by user c#

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C#

ASP.NET

SQL

Hello. I have this interface Dropbox - PUBLIC PHOTOS FOR FORUMS[^]

I created this in order for our HR Staff to filter employees and generate report according to their requirement (e.g All Faculty in Middle School, all american teachers, etc). I used to call this Flexible Employee Filtering

However, Do you have any suggestion on how to make this work without any convenience especially when using OR in WHERE clause? This is one of my dilemma

This is my code so far

public void downloadOutput()
   {
       List<OrderFields> listOrderBy = OrderBy(); //PUTTING ALL FIELDS IN ORDER DEPENDING ON THE USER'S SELECTION IN ORDER FIELD TO BE USED IN 'ORDER BY'
       List<string> listFields = constructFieldNames(); //TO BE USED IN 'SELECT' ,FIELDS TO BE SHOWN,values from FIELDS interface
       List<string> listCondition = constructCondition(); //TO BE USED IN 'WHERE' CLAUSE, values from PARAMETERS INTERFACE
       string strFieldsToShow = string.Join(",", listFields);
       string strCondition = string.Join(" ", listCondition);
       string strOrderByFields = "";
       var newOrderByFields = new List<OrderFields>();
       newOrderByFields = listOrderBy;
       for (int i = 0; i <= listOrderBy.Count - 1; i++)
       {
           strOrderByFields += newOrderByFields[i].OrderField.ToString()+",";
       }
       strOrderByFields = strOrderByFields.Trim(',');
       string finalquery = "Select "+strFieldsToShow+" FROM "+
                       "EmploymentInfo LEFT JOIN EmpPersonalInfo "+
                       "ON EmploymentInfo.EmployeeNo=EmpPersonalInfo.EmployeeNo "+
                       "LEFT JOIN tblEmployeeMainInfo ON EmpPersonalInfo.EmployeeNo = tblEmployeeMainInfo.EmployeeCode "+
                       "LEFT JOIN EmploymentHistory ON EmpPersonalInfo.EmployeeNo = EmploymentHistory.EmployeeNo "+
                       "LEFT JOIN viewEmployeeApprover ON EmpPersonalInfo.EmployeeNo = viewEmployeeApprover.EmployeeNo "+
                       "LEFT JOIN EmployeePayType ON EmpPersonalInfo.EmployeeNo = EmployeePayType.EmployeeCode";

       if (strCondition.Trim() != "")
       {
           finalquery += " where " + strCondition;
       }

       if (strOrderByFields.Trim() != "")
       {
           finalquery += " order by " + strOrderByFields;
       }
       using (SqlConnection con = new SqlConnection(DAO.ConnectionString))
       {
           con.Open();
           using (SqlCommand cmd = new SqlCommand(finalquery, con))
           {
               SqlDataAdapter da = new SqlDataAdapter(cmd);
               DataTable dt = new DataTable();
               da.Fill(dt);
               exportToExcel(dt);
           }
       }
   }

And these are the output of the strings.

strFieldsToShow = "EmpPersonalInfo.EmployeeNo, EmpPersonalInfo.LastName, EmpPersonalInfo.FirstName, tblEmployeeMainInfo.BranchCode"

strCondition = "EmploymentHistory.Status='TRUE' AND tblEmployeeMainInfo.LevelCode like 'FACULTY%'"

strOrderByFields="EmpPersonalInfo.Lastname,EmpPersonalInfo.FirstName,EmpPersonalInfo.BranchCode,EmpPersonalInfo.EmployeeNo"

Please note that TABLE NAMES are values of dropdownlist which I created in other class.

What I have tried:

I have tried the codes above, it is working except for when user selects OR for the where clause.