system/Model.php
public function findColumn(string $columnName)
	{
		if (strpos($columnName, ',') !== false)
		{
			throw DataException::forFindColumnHaveMultipleColumns();
		}

		$resultSet = $this->select($columnName)
						  ->asArray()
						  ->find();

		return (! empty($resultSet)) ? array_column($resultSet, $columnName) : null;
	}
public function findColumn(string $columnName)
	{
		if (strpos($columnName, ',') !== false)
		{
			throw DataException::forFindColumnHaveMultipleColumns();
		}

		$resultSet = $this->select($columnName)
						  ->asArray()
						  ->find();

		return (! empty($resultSet)) ? array_column($resultSet, $columnName) : null;
	}
Fetches the column of database from $this->table

@param string $columnName

@return array|null   The resulting row of data, or null if no data found.