Delete empty fields in PHP array

With php and html I am making a page that contains a form, through which a database is consulted in Firebird.

I have two models:

• The first , works correctly, since it only does search queries and updates ONLY one record each time:

  //Por un lado tengo el formulario en html (pongo sólo el botón y la cabecera):
  
  form name="formulario" id="formulario" method="post"
  
  input type="submit" name="btn1" value="Actualizar" 
  
  //Y por otro lado (en la misma página) tengo el .php
  
  if (isset($_POST["btn1"])){
   $btn=$_POST["btn1"];
  
      if ($btn=="Actualizar"){
      $sqlStr= ' ';
  
       //Saco un nuevo array con los campos vacíos del formulario eliminados.
        if (!empty($POST_){
        unset ($_POST['btn1']);
        for each ($_POST as $key => $value) {
                     if (trim($value) != '') {
                       $sqlArr[]="$key='$value'";
  }}}
  
       //convierto array a string
      $sqlStr=implode(", ", $sqlArr);
  
     $sql = "update tabla set $sqlStr";
  

In short, doing this I update the registry without problems, because even if the fields are empty, the last string remains as I want (ID = '1', NAME = '2' ...).

• The second method is to do a search and print more than one record. Each resulting row will have an "update" button next to it, which will update that row. The code I have is the following:

list.php:

//en php:

if (isset($_POST["btn1"])){
     $btn=$_POST["btn1"];

        if ($btn=="Buscar"){

   $sql="consulta sql"

<form name='ejecuta' action='ejecuta2.php' method='post'>

<tr>
<td>ID_AGENTE</td>
<td>ID_COLABORADOR</td>
<td>ID_PERSONA</td>
</tr>

$i=0;

    while ($resul=ibase_fetch_row($cs)){
   $var=$resul[0];
   $var1='resul[1];
   $var2=$resul[2];

echo "<tr>
<td>
<input name='ID_AGENTE[$i]' value='".$var."' /></td>
<input name='ID_ COLABORADOR[$i]' value='".$var1."' /></td>
<input name='ID_PERSONA[$i]' value='".$var2."' /></td>
<td><input type="submit" name='seleccion[$i]' value='Actualizar'></td>
</tr>";
$i++;
}
echo "</table></form>;

This works relatively well for me, since it shows the form well and when it comes to doing the search it shows all the records on the screen.

The problem comes when using the submit with the name select [$ i] and value Update .

I tried to base myself on the php code of the first model, doing this:

run2.php:

<?php

foreach ($_POST['seleccion'] as $indice => $valor){
//verificamos que se ha dado al boton actualizar.
$opcion=substr ($_POST['seleccion'][$indice],0,-1); //extraemos la parte de la cadena que será "Actualizar".

switch ($opcion) {

     case: "Actualizar":

          if (!empty($_POST)){

               if (trim($valor) != ''){
              $sqlArr[]="$indice='$valor'";}}

print_r $sqlArr;

     sql="$sql = "update tabla set $sqlStr";
    break;

?>

Surely there is something wrong when I pass my code to this, but in conclusion, what I do not know is how to eliminate empty fields in the array according to the form I have in the second model so that at the end I have a string of the type : ID = '1', NAME = 'JOSE'.

I have tried to put it in several ways and always always, when doing the procedure of deletion with the array, I always get: 0 = 'Update'.