Join query in Windows Application

Example 1

query = "select Distinct IBS_ITEM_MST.Item_Cde from IBS_ITEM_MST,IBS_SALESORDER,IBS_SALESORDER_DETAILS where IBS_SALESORDER.SO_No = IBS_SALESORDER_DETAILS.SO_No AND IBS_SALESORDER_DETAILS.Item_Code = IBS_ITEM_MST.Item_Code AND IBS_SALESORDER.Cust_Id = '" + sid + "' AND IBS_ITEM_MST.Item_Cde Like '" + str + "%' and IBS_SALESORDER_DETAILS.Comp_Code ='" + compid + "' and IBS_SALESORDER_DETAILS.Year_Code = '" + yearid + "' and IBS_SALESORDER_DETAILS.SO_Billed = 'N' and (IBS_SALESORDER_DETAILS.SO_Bill_Type = 'N' or IBS_SALESORDER_DETAILS.SO_Bill_Type = 'I')";

Example 2

string query = "select IBS_ITEM_MST.Item_Name,IBS_ITEM_MST.Item_Cde,IBS_ITEM_MST.Item_UOM,IBS_ITEM_MST.Item_UOM1,IBS_ITEM_MST.Item_Srate,IBS_ITEM_MST.Item_Code from IBS_ITEM_MST where Item_Cde = '" + a + "'";