<apex:page id="myPage" controller="DynamicSearchPatientClass" sidebar="false">
    <script type="text/javascript">
    function doSearch() {
        searchServer(
            document.getElementById("myPage:myFrm:pbMain:pbsMain:Name").value,
            document.getElementById("myPage:myFrm:pbMain:pbsMain:Gender").value,
            document.getElementById("myPage:myFrm:pbMain:pbsMain:Email").value,
            document.getElementById("myPage:myFrm:pbMain:pbsMain:Doctor").value);
    }
    </script>    
    <apex:form id="myFrm">
        <apex:actionFunction name="searchServer" action="{!runSearch}" rerender="result">
            <apex:param name="Name" value="" />
            <apex:param name="Gender" value="" />
            <apex:param name="Email" value="" />
            <apex:param name="Doctor" value="" />
        </apex:actionFunction>       
        <apex:pageBlock id="pbMain">
            <apex:pageBlockSection id="pbsMain" title="Patient Search" collapsible="false" columns="2" >
                Patient Name<apex:inputText value="{!objPatients.Name}" id="Name" onkeyup="doSearch();"/>
                Gender<apex:inputText value="{!objPatients.Gender__c}" id="Gender" onchange="doSearch();"/>
                Email<apex:inputText value="{!objPatients.Email__c}" id="Email" onkeyup="doSearch();"/>
                Doctor Name<apex:inputText value="{!objPatients.Doctor__c }" id="Doctor" onchange="doSearch();"/>
            </apex:pageBlockSection>            
            <apex:pageBlockSection title="Patient Details" id="result" >
                <apex:pageBlockTable value="{!patients}" var="p" id="result2">
                    <apex:column value="{!p.Name}"/>
                    <apex:column value="{!p.Gender__c}"/>
                    <apex:column value="{!p.Email__c}"/>
                    <apex:column value="{!p.Doctor__c }"/>
                </apex:pageBlockTable>
            </apex:pageBlockSection>
        </apex:pageBlock>
    </apex:form>
</apex:page>

public with sharing class DynamicSearchPatientClass {
    Private string soql {get;set;}
    public Patient__c objPatients {get;set;}
    public List<Patient__c> patients {get;set;}
    public String sortDir{
        get { if (sortDir == null) { sortDir = 'asc'; }
        return sortDir;}
        set;
    }    
    public String sortField {
        get {if  ( sortField == null) {
        sortField = 'Name'; } return sortField; }
        set;
    }    
    public void runQuery() {
        try {
            patients= Database.query(soql + ' order by ' + sortField + ' ' + sortDir + ' limit 20 ');
            system.debug('>>>>>>4' +patients);
        }
        catch (Exception e) {
            ApexPages.addMessage(new ApexPages.Message(ApexPages.Severity.ERROR, ' OOOps! ') );
        }
    }    
    public DynamicSearchPatientClass(){
        soql='select name,Email__c,Gender__c,Doctor__c from patient__c where patient__c.Name != null';
        system.debug('>>>>>>' +soql);
        runQuery();    
    }    
    public PageReference runSearch(){
        String Name = Apexpages.currentPage().getParameters().get('Name');
        String Gender = Apexpages.currentPage().getParameters().get('Gender');
        String Email = Apexpages.currentPage().getParameters().get('Email');
        String Doctor= Apexpages.currentPage().getParameters().get('Doctor');        
        soql='select name,Email__c,Gender__c,Doctor__c from patient__c where Name != null';   
        system.debug('>>>>>>3' +soql);
        if (!Name.equals(''))
            soql += ' and Name LIKE \''+String.escapeSingleQuotes(Name)+'%\'';
            system.debug('>>>>>>1' +soql);
        if (!Email.equals(''))
            soql += ' and Email__c LIKE \''+String.escapeSingleQuotes(Email)+'%\'';
        if (!Gender.equals(''))
            system.debug('>>>>>>2' +soql);
            soql += ' and Gender__c LIKE \''+String.escapeSingleQuotes(Gender)+'%\'';
        if (!Doctor.equals(''))
            soql += ' and Doctor__c LIKE \''+String.escapeSingleQuotes(Doctor)+'%\'';        
        runQuery();        
        return null;    
    }
}