How to fetch perticular column data of table?

Question

Currently I am using API for fetch the data.
I am creating an extension. I want to fetch the particular column's data from the table. How will I get the data?

//getting id and name
public static function getName(){
 $data = ($id,$name);
  $result = civicrm_api3('Emp', 'get', [
      'sequential' => 1,
      'return' => ["id", "name"],
  ]);

  foreach ($result['values'] as $value) {
      $data[$id] += $value['id'];
      $data[$name] += $value['name'];

  }
  return $data;
} 

Select option using BuildQuickForm

$this->add('select', 
      'name',         //field type 
      'name', //field label
      $this->getName() //list (id, name) 
      );

Answer 1

For every table CiviCRM has api, you can use following method to retrieve data by specifying return in api params.

1 - Get - Returns one or more results and with N number of columns

$result = civicrm_api3('Contact', 'get', [
  'return' => ["id", "display_name"],
  'contact_sub_type' => "Parent",
]);

2 - GetValue - Returns only single result and with single column (make sure to use id in filer or limit =1 else the api will throw error if the api returns more than one results)

$result = civicrm_api3('Contact', 'getvalue', [
  'return' => "display_name",
  'id' => 1,
]);

3 - GetSingle - Returns only single result and with N number of columns (make sure to use id in filer or limit =1 else the api will throw error if the api returns more than one results)

$result = civicrm_api3('Contact', 'getsingle', [
  'return' => ["display_name", "email"],
  'id' => 1,
]);

Incase if you want to retrieve from custom table created using extension then you will need to make sure you have

1. New entity defined -
2. DAO for the table
3. api with create, delete and get action

You can use Civix to create new entity which will create above 3 points automatically for you.

Then you can use below snippet to build your select field

    $this->add('select', 
      'name',         //field type 
      ts('Name'), //field label
      CRM_Utils_Array::collect('name', civicrm_api3('Emp', 'get', [
        'return' => ["id", "name"],
      ])['values']) //list (id, name) 
    );

HTH

Pradeep