diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7f07ac7..6937e05 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,10 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
 
+## [4.2.1] - 2018-12-22
+### Fixed
+- SQL error when same column names given in several tables
+
 ## [4.2.0] - 2018-12-16
 ### Added
 - Support for Nextcloud 15
@@ -108,6 +112,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 ### Changed
 - Supported version of ownCloud, Nextcloud: ownCloud 10, Nextcloud 12
 
+[4.2.1]: https://github.com/nextcloud/user_sql/compare/v4.2.0...v4.2.1
 [4.2.0]: https://github.com/nextcloud/user_sql/compare/v4.1.0...v4.2.0
 [4.1.0]: https://github.com/nextcloud/user_sql/compare/v4.0.1...v4.1.0
 [4.0.1]: https://github.com/nextcloud/user_sql/compare/v4.0.0...v4.0.1
diff --git a/appinfo/info.xml b/appinfo/info.xml
index 83ded89..6652457 100644
--- a/appinfo/info.xml
+++ b/appinfo/info.xml
@@ -8,7 +8,7 @@
         Retrieve the users and groups info. Allow the users to change their passwords.
         Sync the users' email addresses with the addresses stored by Nextcloud.
     </description>
-    <version>4.2.0</version>
+    <version>4.2.1</version>
     <licence>agpl</licence>
     <author>Marcin Łojewski</author>
     <author>Andreas Böhler</author>
diff --git a/lib/Query/QueryProvider.php b/lib/Query/QueryProvider.php
index cd027d0..0a1bf76 100644
--- a/lib/Query/QueryProvider.php
+++ b/lib/Query/QueryProvider.php
@@ -87,80 +87,80 @@ class QueryProvider implements \ArrayAccess
         $uidParam = Query::UID_PARAM;
 
         $groupColumns
-            = "$gGID AS gid, " .
-            (empty($gName) ? $gGID : $gName) . " AS name, " .
-            (empty($gAdmin) ? "false" : $gAdmin) . " AS admin";
+            = "g.$gGID AS gid, " .
+            (empty($gName) ? "g." . $gGID : "g." . $gName) . " AS name, " .
+            (empty($gAdmin) ? "false" : "g." . $gAdmin) . " AS admin";
         $userColumns
-            = "$uUID AS uid, " .
-            (empty($uName) ? $uUID : $uName) . " AS name, " .
-            (empty($uEmail) ? "null" : $uEmail) . " AS email, " .
-            (empty($uQuota) ? "null" : $uQuota) . " AS quota, " .
-            (empty($uHome) ? "null" : $uHome) . " AS home, " .
-            (empty($uActive) ? "true" : $uActive) . " AS active, " .
-            (empty($uAvatar) ? "false" : $uAvatar) . " AS avatar, " .
-            (empty($uSalt) ? "null" : $uSalt) . " AS salt";
+            = "u.$uUID AS uid, " .
+            (empty($uName) ? "u." . $uUID : "u." . $uName) . " AS name, " .
+            (empty($uEmail) ? "null" : "u." . $uEmail) . " AS email, " .
+            (empty($uQuota) ? "null" : "u." . $uQuota) . " AS quota, " .
+            (empty($uHome) ? "null" : "u." . $uHome) . " AS home, " .
+            (empty($uActive) ? "true" : "u." . $uActive) . " AS active, " .
+            (empty($uAvatar) ? "false" : "u." . $uAvatar) . " AS avatar, " .
+            (empty($uSalt) ? "null" : "u." . $uSalt) . " AS salt";
 
         $this->queries = [
             Query::BELONGS_TO_ADMIN =>
-                "SELECT COUNT($gGID) > 0 AS admin " .
-                "FROM $group, $userGroup " .
-                "WHERE $ugGID = $gGID " .
-                "AND $ugUID = :$uidParam " .
-                "AND $gAdmin",
+                "SELECT COUNT(g.$gGID) > 0 AS admin " .
+                "FROM $group g, $userGroup ug " .
+                "WHERE ug.$ugGID = g.$gGID " .
+                "AND ug.$ugUID = :$uidParam " .
+                "AND g.$gAdmin",
 
             Query::COUNT_GROUPS =>
-                "SELECT COUNT($ugGID) " .
-                "FROM $userGroup " .
-                "WHERE $ugGID = :$gidParam " .
-                "AND $ugUID " .
+                "SELECT COUNT(ug.$ugGID) " .
+                "FROM $userGroup ug " .
+                "WHERE ug.$ugGID = :$gidParam " .
+                "AND ug.$ugUID " .
                 "LIKE :$searchParam",
 
             Query::COUNT_USERS =>
-                "SELECT COUNT($uUID) AS count " .
-                "FROM $user " .
-                "WHERE $uUID LIKE :$searchParam",
+                "SELECT COUNT(u.$uUID) AS count " .
+                "FROM $user u " .
+                "WHERE u.$uUID LIKE :$searchParam",
 
             Query::FIND_GROUP =>
                 "SELECT $groupColumns " .
-                "FROM $group " .
-                "WHERE $gGID = :$gidParam",
+                "FROM $group g " .
+                "WHERE g.$gGID = :$gidParam",
 
             Query::FIND_GROUP_USERS =>
-                "SELECT $ugUID AS uid " .
-                "FROM $userGroup " .
-                "WHERE $ugGID = :$gidParam " .
-                "AND $ugUID " .
+                "SELECT ug.$ugUID AS uid " .
+                "FROM $userGroup ug " .
+                "WHERE ug.$ugGID = :$gidParam " .
+                "AND ug.$ugUID " .
                 "LIKE :$searchParam " .
-                "ORDER BY $ugUID",
+                "ORDER BY ug.$ugUID",
 
             Query::FIND_GROUPS =>
                 "SELECT $groupColumns " .
-                "FROM $group " .
-                "WHERE $gGID LIKE :$searchParam " .
-                "ORDER BY $gGID",
+                "FROM $group g " .
+                "WHERE g.$gGID LIKE :$searchParam " .
+                "ORDER BY g.$gGID",
 
             Query::FIND_USER =>
-                "SELECT $userColumns, $uPassword AS password " .
-                "FROM $user " .
-                "WHERE $uUID = :$uidParam",
+                "SELECT $userColumns, u.$uPassword AS password " .
+                "FROM $user u " .
+                "WHERE u.$uUID = :$uidParam",
 
             Query::FIND_USER_CASE_INSENSITIVE =>
-                "SELECT $userColumns, $uPassword AS password " .
-                "FROM $user " .
-                "WHERE lower($uUID) = lower(:$uidParam)",
+                "SELECT $userColumns, u.$uPassword AS password " .
+                "FROM $user u " .
+                "WHERE lower(u.$uUID) = lower(:$uidParam)",
 
             Query::FIND_USER_GROUPS =>
                 "SELECT $groupColumns " .
-                "FROM $group, $userGroup " .
-                "WHERE $ugGID = $gGID " .
-                "AND $ugUID = :$uidParam " .
-                "ORDER BY $gGID",
+                "FROM $group g, $userGroup ug " .
+                "WHERE ug.$ugGID = g.$gGID " .
+                "AND ug.$ugUID = :$uidParam " .
+                "ORDER BY g.$gGID",
 
             Query::FIND_USERS =>
                 "SELECT $userColumns " .
-                "FROM $user " .
-                "WHERE $uUID LIKE :$searchParam " .
-                "ORDER BY $uUID",
+                "FROM $user u " .
+                "WHERE u.$uUID LIKE :$searchParam " .
+                "ORDER BY u.$uUID",
 
             Query::UPDATE_DISPLAY_NAME =>
                 "UPDATE $user " .