public function get_unique_primary($table): ?string
  {
    if ( ($keys = $this->get_keys($table)) &&
      isset($keys['keys']['PRIMARY']) &&
      (\count($keys['keys']['PRIMARY']['columns']) === 1) ){
      return $keys['keys']['PRIMARY']['columns'][0];
    }
    return null;
  }
public function get_unique_primary($table): ?string
  {
    if ( ($keys = $this->get_keys($table)) &&
      isset($keys['keys']['PRIMARY']) &&
      (\count($keys['keys']['PRIMARY']['columns']) === 1) ){
      return $keys['keys']['PRIMARY']['columns'][0];
    }
    return null;
  }
public function get_unique_primary ( $ table ) : ? string { if ( ( $ keys = $ this -> get_keys ( $ table ) ) && isset ( $ keys [ 'keys' ] [ 'PRIMARY' ] ) && ( \ count ( $ keys [ 'keys' ] [ 'PRIMARY' ] [ 'columns' ] ) === 1 ) ) { return $ keys [ 'keys' ] [ 'PRIMARY' ] [ 'columns' ] [ 0 ] ; } return null ; }
Return the unique primary key of the given table.

```php
\bbn\x::dump($db->get_unique_primary('table_users'));
// (string) id
```

@param string $table The table's name
@return null|string
Return the unique primary key of the given table .