title: check if value exist in $_POST[''] is identical
body: <p>I am working on Ajax.i have multiple select box now i want recall same page again and again but problem is that we have lots sql query.with the of if condition i select query according to my need.now i want check like if ($_POST['field'] contain state or region );
  ajax part:-</p>
  
  <pre><code>$('#country').change(function()
          {
              var id=$("#country").val();
              var dataString = 'id='+ id;
  
              $.ajax
              ({
                  type: "POST",
                  url: "ajax_centre.php",
                  data: {state:dataString,field:'state'},
                  cache: false,
                  success: function(html)
                  {
                  $("#state").html(html);
                  } 
              });
          });
          $('#state').change(function()
          {
              var state_id=$('#state').val();
              var country_id=$('#country').val();
              var dataString = 'state_id='+ state_id;
              var country_id = 'country_id='+ country_id;
  
  
              $.ajax
              ({
                  type: "POST",
                  url: "ajax_centre.php",
                  data: {country:country_id,state:dataString,field:'region'},
                  cache: false,
                  success: function(html)
                  {
                  $("#region").html(html);
                  } 
              });
  
          }); 
  </code></pre>
  
  <p>in upper part i pass field:state and field:region now i want to select my on behalf of that
  //ajax_centre.php:-</p>
  
  <pre><code>if($_POST['field']='state')
  {
     //execute query
  
  }
  
  if($_POST['field']='region')
  {
      //execute query
  }
  </code></pre>
  
  <p>is this possible i know isset() but i have to differentiate each other  </p>
  
  <p>i finally i find the bug problem exist in passing post value correct script:-</p>
  
  <pre><code>$('#country').change(function()
          {
              var id=$("#country").val();
              //var dataString = 'id='+ id;
  
              $.ajax
              ({
                  type: "POST",
                  url: "ajax_centre.php",
                  data: {id:id,field:'state'},
                  cache: false,
                  success: function(html)
                  {
                  $("#state").html(html);
                  } 
              });
          });
          $('#state').change(function()
          {
              var state_id=$('#state').val();
              var country_id=$('#country').val();
              //var dataString = 'state_id='+ state_id;
              //var country_id = 'country_id='+ country_id;
  
  
              $.ajax
              ({
                  type: "POST",
                  url: "ajax_centre.php",
                  data: {con_id:country_id,sta_id:state_id,field:'region'},
                  cache: false,
                  success: function(html)
                  {
                  $("#region").html(html);
                  } 
              });
  
          }); 
  </code></pre>
  
  <p>one think i got both operator work in my case "==" and "===".</p>