I am getting this error ,while i was fetching data from Account sobject using dynamic query based on option selected by the user.
**********************************************************************Apex class ****************************************************************************
public class Dyanmic1 {
    
    public List<SelectOption>     options     {set;get;}
    public List<String>         selected     {set;get;}
    public List<Account>         accounts     {set;get;}
    public Dyanmic1(){
        options  = new List<SelectOption>();
        selected = new List<String>();
        accounts  = new List<Account>();
        List<String> fields = new List<String>{'Name','Industry','Rating','Phone'};
            for(String s : fields){
                SelectOption sop = new SelectOption(s,s);
                options.add(sop);
            }
        
    }
    public void go(){
        String query= 'Select ID';
        for(String s: selected){
            query = query+','+ s ;
            
        }
        query = query+'FROM Account';
        accounts = Database.query(query);
    }
    
}
*************************************************************VF Page*******************************************************************************
<apex:page controller="Dyanmic1">
    <apex:form>
    <apex:selectList multiSelect="true" value="{!selected}" >
        <apex:selectOptions value="{!options}" />
    </apex:selectList>
    <apex:commandButton value="Go" action ="{!go}"/>
    <apex:pageBlock>
    <apex:dataTable value="{!accounts}" var="a">
        <apex:repeat value="{!selected}" var="f">
            <apex:column value="{!a[f]}"/>
        </apex:repeat>
    </apex:dataTable> 
   </apex:pageBlock>
   </apex:form>
</apex:page>
***********************************************************************************************
Please help.
Thanks in advance,
Venkat.