protected function getOperator(string $str, bool $list = false)
	{
		static $_operators;

		if (empty($_operators))
		{
			$_les       = ($this->db->likeEscapeStr !== '') ? '\s+' . preg_quote(trim(sprintf($this->db->likeEscapeStr, $this->db->likeEscapeChar)), '/') : '';
			$_operators = [
				'\s*(?:<|>|!)?=\s*', // =, <=, >=, !=
				'\s*<>?\s*', // <, <>
				'\s*>\s*', // >
				'\s+IS NULL', // IS NULL
				'\s+IS NOT NULL', // IS NOT NULL
				'\s+EXISTS\s*\(.*\)', // EXISTS(sql)
				'\s+NOT EXISTS\s*\(.*\)', // NOT EXISTS(sql)
				'\s+BETWEEN\s+', // BETWEEN value AND value
				'\s+IN\s*\(.*\)', // IN(list)
				'\s+NOT IN\s*\(.*\)', // NOT IN (list)
				'\s+LIKE\s+\S.*(' . $_les . ')?', // LIKE 'expr'[ ESCAPE '%s']
				'\s+NOT LIKE\s+\S.*(' . $_les . ')?', // NOT LIKE 'expr'[ ESCAPE '%s']
			];
		}

		return preg_match_all('/' . implode('|', $_operators) . '/i', $str, $match) ? ($list ? $match[0] : $match[0][count($match[0]) - 1]) : false;
	}