controlador-descarga/controllers/EstacionController.php

<?php

namespace app\controllers;

use app\components\data\Respuesta;
use app\components\rest\JsonController;
use yii\db\Query;
use yii\filters\AccessControl;

class EstacionController extends JsonController {

  public function behaviors() {
    return [
      'access' => [
        'class' => AccessControl::className(),
        'only' => ['por-pc'],
        'rules' => [
          [
            'actions' => ['por-pc'],
            'allow' => true,
            'roles' => ['@'],
          ],
        ],
      ],
    ];
  }

  public function actionPorPc() {
    $req = \Yii::$app->getRequest();
    $pc = trim($req->get("pc", ""));

    if($pc === "") {
      return (new Respuesta())
        ->esError()
        ->mensaje("Debe enviar el PC");
    }

    $query = (new Query())
      ->distinct()
      ->select([
        "estacion as [[clave]]",
        "ciudad as [[idCiudad]]",
        "ciudad || '-' || estacion as [[key]]",
      ])
      ->from("Descarga")
      ->andWhere(["pc" => $pc]);

    return (new Respuesta($query, -1));
  }

}