add an option to disable DISTINCT on headlines query (unless it's Labels category)

classes/feeds.php

@@ -1621,6 +1621,11 @@ class Feeds extends Handler_Protected {
 				$distinct_qpart = "DISTINCT"; //fallback
 			}
 
+			// except for Labels category
+			if (get_pref(Prefs::HEADLINES_NO_DISTINCT) && !($feed == -2 && $cat_view)) {
+				$distinct_qpart = "";
+			}
+
 			if (!$search && !$skip_first_id_check) {
 				// if previous topmost article id changed that means our current pagination is no longer valid
 				$query = "SELECT

classes/pref/prefs.php

@@ -63,6 +63,7 @@ class Pref_Prefs extends Handler_Protected {
 				Prefs::SHORT_DATE_FORMAT,
 				'BLOCK_SEPARATOR',
 				Prefs::SSL_CERT_SERIAL,
+				Prefs::HEADLINES_NO_DISTINCT,
 			]
 		];
 
@@ -97,7 +98,8 @@ class Pref_Prefs extends Handler_Protected {
 			Prefs::USER_TIMEZONE => array(__("Time zone")),
 			Prefs::VFEED_GROUP_BY_FEED => array(__("Group by feed"), __("Group multiple-feed output by originating feed")),
 			Prefs::USER_LANGUAGE => array(__("Language")),
-			Prefs::USER_CSS_THEME => array(__("Theme"))
+			Prefs::USER_CSS_THEME => array(__("Theme")),
+			Prefs::HEADLINES_NO_DISTINCT => array(__("Don't enforce DISTINCT headlines"), __("May produce duplicate entries")),
 		];
 
 		// hidden in the main prefs UI (use to hide things that have description set above)

classes/prefs.php

@@ -56,6 +56,7 @@ class Prefs {
 	const USER_LANGUAGE = "USER_LANGUAGE";
 	const DEFAULT_SEARCH_LANGUAGE = "DEFAULT_SEARCH_LANGUAGE";
 	const _PREFS_MIGRATED = "_PREFS_MIGRATED";
+	const HEADLINES_NO_DISTINCT = "HEADLINES_NO_DISTINCT";
 
 	private const _DEFAULTS = [
 		Prefs::PURGE_OLD_DAYS => [ 60, Config::T_INT ],
@@ -112,6 +113,7 @@ class Prefs {
 		Prefs::USER_LANGUAGE => [ "" , Config::T_STRING ],
 		Prefs::DEFAULT_SEARCH_LANGUAGE => [ "" , Config::T_STRING ],
 		Prefs::_PREFS_MIGRATED => [ false, Config::T_BOOL ],
+		Prefs::HEADLINES_NO_DISTINCT => [ false, Config::T_BOOL ],
 	];
 
 	const _PROFILE_BLACKLIST = [