protected function getKeySql($columns)
	{
		// TODO Error checking on array and element types.

		$kNonUnique = (string) $columns[0]['Non_unique'];
		$kName      = (string) $columns[0]['Key_name'];
		$kColumn    = (string) $columns[0]['Column_name'];

		$prefix = '';

		if ($kName === 'PRIMARY')
		{
			$prefix = 'PRIMARY ';
		}
		elseif ($kNonUnique == 0)
		{
			$prefix = 'UNIQUE ';
		}

		$nColumns = \count($columns);
		$kColumns = array();

		if ($nColumns === 1)
		{
			$kColumns[] = $this->db->quoteName($kColumn);
		}
		else
		{
			foreach ($columns as $column)
			{
				$kColumns[] = (string) $column['Column_name'];
			}
		}

		$sql = $prefix . 'KEY ' . ($kName !== 'PRIMARY' ? $this->db->quoteName($kName) : '') . ' (' . implode(',', $kColumns) . ')';

		return $sql;
	}