Dynamic soql With Schema and metadata programing

Step 1: Create a  VF page in which Object should be list of picklist fields obtained from the schema

Step2 : When ever we  select the particular object from the picklist list of object based on the object what we have selected we have to get the corresponding list of fields

Displayed in the multiselect picklist field

Once you select the list of fields from the multiselect picklist field then click on getQuery

Apex Class :

public  class SchemaDynamicExample {

     public Map<String,Schema.SobjectType> objMap {Set;get;}

     public Map<String,Schema.SobjectField> fldMap {set;get;}

     public List<String> objList {Set;get;}

     public List<SelectOption> objOptions{set;get;}

     public String objselected{set;get;}

     public List<String> fldList{set;get;}

     public Set<String> nsflds{set;get;}

     public Set<String> sflds{Set;get;}

     public List<SelectOption> nsoptions{set;get;}

     public List<SelectOption> soptions{set;get;}

     public List<String> selected{set;get;}

     public List<String> removed{set;get;}

     public List<Account> accs{set;get;}

     public String query {Set;get;}

     public List<String> pbtflds{Set;get;}

     public SchemaDynamicExample(){

          objList=new List<String>();

          objOptions=new List<SelectOption>();

          fldList=new List<String>();

          nsflds=new Set<String>();

          sflds=new Set<String>();

          nsoptions=new List<SelectOption>();

          soptions=new List<SelectOption>();

          selected=new List<String>();

          removed=new List<String>();

          getObjects();

          SelectOption op=new SelectOption('none','-none-');

          nsoptions.add(op);

          soptions.add(op);

     }

     public void getObjects(){

          objMap=Schema.getGlobalDescribe();

          Set<String> keys=objMap.keySet();

          objList.addAll(keys);

          objList.sort();

          SelectOption op=new SelectOption('none','-None-');

          objoptions.add(op);

          for(String s:objList){

              selectOption op1=new SelectOption(s,s);

              objOptions.add(op1);

          }

     }

     public void getResults(){

          query='select id';

          for(string s:sflds){

              if(s!='id'){

                   query=query+','+s;

              }

          }

          query=query+' from Account';

          accs=Database.query(query);

          pbtflds=new List<String>();

          pbtflds.addAll(sflds);

     }

     public void getFields(){

          Schema.DescribeSobjectResult result=objMap.get(objSelected).getDescribe();

          fldmap=result.fields.getMap();

          Set<String> keys=fldmap.keySet();

          fldList.addAll(keys);

          fldList.sort();

          nsflds.addAll(fldList);

          multiselect();

     }

    public void  multiselect(){

          nsoptions.clear();

          soptions.clear();

         

          List<String> slist=new List<String>();

          slist.addAll(sflds);

          slist.sort();

          List<String> nslist=new List<String>();

          nslist.addAll(nsflds);

          nslist.sort();

          for(String s1:nslist){

              SelectOption op1=new SelectOption(s1,s1);

              nsoptions.add(op1);

          }

          for(String s2:slist){

              SelectOption op2=new SelectOption(s2,s2);

              soptions.add(op2);

          }   

   }

   public void addEle(){

          nsflds.removeAll(Selected);

          sflds.addAll(selected);

          multiselect();

   }

   public void removeEle(){

          sflds.removeAll(removed);

          nsflds.addAll(removed);

          multiSelect();

   }

}

Visualforce page:

<apex:page controller="SchemaDynamicExample" >

     <apex:form>

          <apex:pageBlock title="Schema Dynamic List">

              <apex:pageBlockSection>

                   <apex:pageBlockSectionItem >

                        <apex:outputLabel value="Objects" />

                        <apex:selectList value="{!objSelected}" size="1">

                             <apex:selectOptions value="{!objOptions}" />

                             <apex:actionSupport event="onchange" action="{!getFields}" reRender="pg"/>

                        </apex:selectList>

                   </apex:pageBlockSectionItem>

                   <apex:pageBlockSectionItem>

                        <apex:panelGrid id="pg" columns="3">

                             <apex:selectList value="{!selected}" multiselect="true" style="width:100px;height:200px;" >

                                  <apex:selectOptions value="{!nsoptions}" />

                             </apex:selectList>

                             <apex:panelGrid columns="1">

                                  <br/>

                                  <apex:commandButton value="Add" action="{!addEle}" reRender="pg" style="width:50px;" />

                                  <br/>

                                  <apex:commandButton value="Del" action="{!removeEle}" reRender="pg" style="width:50px;"/>

                             </apex:panelGrid>

                             <apex:selectList value="{!removed}" multiselect="true" style="width:100px;height:200px;" >

                                  <apex:selectOptions value="{!soptions}" />

                             </apex:selectList>

                        </apex:panelGrid>

                   </apex:pageBlockSectionItem>

                   <apex:commandButton value="GetQuery" action="{!getResults}" reRender="pb2" />

              </apex:pageBlockSection>

          </apex:pageBlock>

          <apex:pageBlock id="pb2">

              <apex:pageBlockTable value="{!accs}" var="a">

                   <apex:repeat value="{!pbtflds}" var="b">

                        <apex:column value="{!a[b]}" />

                   </apex:repeat>

              </apex:pageBlockTable>

          </apex:pageBlock>

     </apex:form> 

</apex:page>