• Dynamic SOQL refers to the creation of a SOQL string at runtime with Apex code. Dynamic SOQL enables you to create more flexible applications. For example, you can create a search based on input from an end user or update records with varying field names.
• To create a dynamic SOQL query at runtime, use the database query method, in one of the following ways.
• Return a single s Object when the query returns a single record:

sObject s = Database.query(string_limit_1);

<apex:page controller="Soql_Example1">
    <apex:form >
      <apex:pageBlock title="Accounts">
          <apex:pageBlockButtons location="top">
              <apex:selectlist size="1" value="{!selected}">
                  <apex:actionSupport event="onchange" action="{!dynamicQuery}" rerender="pb"/>
              <apex:selectOption itemLabel="-None-" itemValue="none"/>
                             <apex:selectOption itemLabel="5" itemValue="5"/>
                             <apex:selectOption itemLabel="10" itemValue="10"/>
                             <apex:selectOption itemLabel="15" itemValue="15"/>
                             <apex:selectOption itemLabel="20" itemValue="20"/>
              </apex:selectlist>
              <apex:inputText size="4" value="{!rows}"/>
          <apex:commandButton value="limit" action="{!setLimit}" rerender="pb"/>
                        <apex:commandButton value="Dynamic_limit" action="{!dynamicSetLimit}" rerender="pb"/>

          </apex:pageBlockButtons>

          <apex:pageblocktable value="{!accs1}" var="a" id="pb">
             <apex:column value="{!a.name}"/>       
                       <apex:column value="{!a.industry}"/>       
          </apex:pageblocktable>
        </apex:pageBlock>
    </apex:form>
</apex:page>

public class Soql_Example1 {
    public list<Account> accs1 {set;get;}
    public  integer rows       {set;get;}
    public string selected     {set;get;}
    
    Public Soql_Example1(){
        accs1=[select id,name,industry from account];
    }
    Public Void setLimit(){
        accs1=[select id,name,industry from account limit 10];  
    }//Dymamic Query
    public Void dynamicSetLimit(){
        accs1=[select id,name,industry from account limit :rows];
    }
    public void dynamicQuery(){
        if(selected!='none'){
        string query = 'select id, name,phone,Industry from Account limit ' +selected;
         accs1=Database.query(query);
        }else{
            accs1=new list<Account>();
        }
    }
}