$connection = Bitrix\Main\Application::getConnection();
$connection->queryExecute("SET sql_mode=''");<pre>[RuntimeException] 
Could not start session because headers have already been sent. &quot;/home/drovo103/drovokol22.ru/bitrix/php_interface/after_connect_d7.php&quot;:4. (0)
/home/drovo103/drovokol22.ru/bitrix/modules/main/lib/session/session.php:151
#0: Bitrix\Main\Session\Session-&gt;start()
	/home/drovo103/drovokol22.ru/bitrix/modules/main/lib/session/kernelsessionproxy.php:47
#1: Bitrix\Main\Session\KernelSessionProxy-&gt;start()
	/home/drovo103/drovokol22.ru/bitrix/modules/main/include.php:185
#2: require_once(string)
	/home/drovo103/drovokol22.ru/bitrix/modules/main/include/prolog_before.php:19
#3: require_once(string)
	/home/drovo103/drovokol22.ru/bitrix/modules/main/include/prolog.php:10
#4: require_once(string)
	/home/drovo103/drovokol22.ru/bitrix/header.php:1
#5: require(string)
	/home/drovo103/drovokol22.ru/index.php:2
----------
</pre>