Already I have a controller for the task as below:
public class ContactListController {
    public List<Contact> ContactList {
        get {
            If(Contact.Account.Name != Null) {
                If(ContactList == Null) {
                    ContactList = [SELECT Name, Account.Name, Phone, Email, MailingCity, MailingState, MailingPostalCode FROM Contact WHERE Account.Name != Null 
                                      ORDER BY Account.Name ASC]; 
                } 
            }
            return ContactList;
        }
           set;
    } 
}

the page for this controller is:
<apex:page controller="ContactListController"> <apex:form > <apex:pageBlock > List Of Contacts with Accounts: <apex:pageBlockTable value="{!ContactList}" var="contact" cellpadding="0" cellspacing="0" width="50%"> <apex:column value="{!contact.Account.Name}" onclick="ascending" ondblclick="descending"/> <apex:column value="{!contact.Name}"/> <apex:column value="{!contact.Phone}"/> <apex:column value="{!contact.Email}"/> <apex:column value="{!contact.MailingCity}"/> <apex:column value="{!contact.MailingPostalCode}"/> <apex:column value="{!contact.MailingState}"/> </apex:pageBlockTable> </apex:pageBlock> </apex:form> </apex:page>


But now i want to dynamic query to the  if I click the mouse to the column of each in the table it's give the ascending order and then I click the double click it's give the descending order for the table data.

thank you 
Mohan Raj