如何逐列名称getJSON和php选择所有项目

I have a getJSON call to a php function that returns all items in a column by the column name. This is the PHP function.

public function getCertsByCategory($certCategory) {
       $connection = $this -> connect();
       return $this -> select("select '.$certCatogory.' from cert_catalog");
    }

This is the function to get the data:

function CertName(certCategory) {
       $('#certificationName').empty();
       console.log(certCategory);
       $.getJSON('json_data.php', { method: 'getCertsByCategory', certCategory: certCategory }, function(data) {
          console.log(data);
          $.each(data, function(key, value) {
             console.log(value);
             $('#certificationName').append('<option value="' + value + '">' + value + '</option>');
          });
       });
     }

Why am I getting back two dots for the values? This is what it looks like in chrome developer tools.

10: Object
..: ".."
__proto__: Object
11: Object
..: ".."
__proto__: Object