From c668e7142113f297355cef791332c89ab9d05d48 Mon Sep 17 00:00:00 2001
From: Max Semenik <maxsem@users.mediawiki.org>
Date: Sat, 17 Oct 2009 12:23:23 +0000
Subject: [PATCH] (bug 20256) Fixed SQL errors on Special:Recentchanges and
 Special:Recentchangeslinked on SQLite backend

---
 RELEASE-NOTES                                   |  2 ++
 includes/db/Database.php                        |  9 +++++++++
 includes/db/DatabaseSqlite.php                  |  9 +++++++++
 includes/specials/SpecialRecentchanges.php      |  6 +++++-
 .../specials/SpecialRecentchangeslinked.php     | 17 ++++++++++++++---
 5 files changed, 39 insertions(+), 4 deletions(-)

diff --git a/RELEASE-NOTES b/RELEASE-NOTES
index 9b0713c988..6fefee4442 100644
--- a/RELEASE-NOTES
+++ b/RELEASE-NOTES
@@ -562,6 +562,8 @@ it from source control: http://www.mediawiki.org/wiki/Download_from_SVN
 * (bug 21116) MediaWiki:Templatesused, MediaWiki:Templatesusedpreview and
   MediaWiki:Templatesusedsection now support plural
 * (bug 21079) There is no more line wrapping between label and field in Special:Log
+* (bug 20256) Fixed SQL errors on Special:Recentchanges and Special:Recentchangeslinked
+  on SQLite backend
 
 == API changes in 1.16 ==
 
diff --git a/includes/db/Database.php b/includes/db/Database.php
index 34e33dbb61..c8deb337e9 100644
--- a/includes/db/Database.php
+++ b/includes/db/Database.php
@@ -1695,6 +1695,15 @@ abstract class DatabaseBase {
 		return $this->limitResult( $sql, $num, 0 );
 	}
 
+	/**
+	 * Returns true if current database backend supports ORDER BY or LIMIT for separate subqueries 
+	 * within the UNION construct.
+	 * @return Boolean
+	 */
+	function unionSupportsOrderAndLimit() {
+		return true; // True for almost every DB supported
+	}
+
 	/**
 	 * Construct a UNION query
 	 * This is used for providing overload point for other DB abstractions
diff --git a/includes/db/DatabaseSqlite.php b/includes/db/DatabaseSqlite.php
index 1eb49108cd..e9fe549e4d 100644
--- a/includes/db/DatabaseSqlite.php
+++ b/includes/db/DatabaseSqlite.php
@@ -299,6 +299,15 @@ class DatabaseSqlite extends DatabaseBase {
 		return - 1;
 	}
 
+	function unionSupportsOrderAndLimit() {
+		return false;
+	}
+
+	function unionQueries( $sqls, $all ) {
+		$glue = $all ? ' UNION ALL ' : ' UNION ';
+		return implode( $glue, $sqls );
+	}
+
 	function wasDeadlock() {
 		return $this->lastErrno() == SQLITE_BUSY;
 	}
diff --git a/includes/specials/SpecialRecentchanges.php b/includes/specials/SpecialRecentchanges.php
index 85ace3cb86..1d38e57d2b 100644
--- a/includes/specials/SpecialRecentchanges.php
+++ b/includes/specials/SpecialRecentchanges.php
@@ -306,7 +306,11 @@ class SpecialRecentChanges extends SpecialPage {
 		// Is there either one namespace selected or excluded?
 		// Tag filtering also has a better index.
 		// Also, if this is "all" or main namespace, just use timestamp index.
-		if( is_null($namespace) || $invert || $opts['tagfilter'] ) {
+		if( is_null($namespace)
+			|| $invert
+			|| $opts['tagfilter'] 
+			|| !$dbr->unionSupportsOrderAndLimit() )
+		{
 			$res = $dbr->select( $tables, '*', $conds, __METHOD__,
 				array( 'ORDER BY' => 'rc_timestamp DESC', 'LIMIT' => $limit ) +
 				$query_options,
diff --git a/includes/specials/SpecialRecentchangeslinked.php b/includes/specials/SpecialRecentchangeslinked.php
index a5bd098f78..d84ffa32b4 100644
--- a/includes/specials/SpecialRecentchangeslinked.php
+++ b/includes/specials/SpecialRecentchangeslinked.php
@@ -144,19 +144,30 @@ class SpecialRecentchangeslinked extends SpecialRecentchanges {
 				}
 			}
 
-			$subsql[] = $dbr->selectSQLText( 
+			if( $dbr->unionSupportsOrderAndLimit())
+				$order = array( 'ORDER BY' => 'rc_timestamp DESC' );
+			else
+				$order = array();
+
+			
+			$query = $dbr->selectSQLText( 
 				array_merge( $tables, array( $link_table ) ), 
 				$select, 
 				$conds + $subconds,
 				__METHOD__, 
-				array( 'ORDER BY' => 'rc_timestamp DESC', 'LIMIT' => $limit ) + $query_options,
+				$order + $query_options,
 				$join_conds + array( $link_table => array( 'INNER JOIN', $subjoin ) )
 			);
+			
+			if( $dbr->unionSupportsOrderAndLimit())
+				$query = $dbr->limitResult( $query, $limit );
+
+			$subsql[] = $query;
 		}
 
 		if( count($subsql) == 0 )
 			return false; // should never happen
-		if( count($subsql) == 1 )
+		if( count($subsql) == 1 && $dbr->unionSupportsOrderAndLimit() )
 			$sql = $subsql[0];
 		else {
 			// need to resort and relimit after union
-- 
2.20.1