Hello

when updating to 2.9 and following the tour to discover the new filter Duplicates on the Batch Manager, an error can be encountered similar to:

Warning:  [mysql error 1064] You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ')
    AND (
      ic.category_id != i.storage_category_id
      OR i.storage_cat' at line 5

SELECT
    DISTINCT(category_id) AS id
  FROM piwigo_image_category AS ic
    JOIN piwigo_images AS i ON i.id = ic.image_id
  WHERE ic.image_id IN (278,293,294,295,296,297,298,299,300,301,302,303,292,291,290,279,280,281,282,283,284,285,286,287,288,289,304,305,306,321,322,323,324,325,326,327,328,329,330,331,320,319,318,307,308,309,310,311,312,313,314,315,316,317,332,223,238,239,240,241,242,243,244,245,246,247,248,237,236,235,224,225,226,227,228,229,230,231,232,233,234,249,250,251,266,267,268,269,270,271,272,273,274,275,276,265,264,263,252,253,254,255,256,257,258,259,260,261,262,277,333,389,404,405,406,407,408,409,410,411,412,413,414,403,402,401,390,391,392,393,394,395,396,397,398,399,400,415,416,417,432,433,434,435,436,437,438,439,440,441,442,431,430,429,418,419,420,4 in /home/bvgicdaf/public_html/piwigo_test/include/dblayer/functions_mysqli.inc.php on line 845


Fatal error: Call to a member function fetch_assoc() on a non-object in /home/bvgicdaf/public_html/piwigo_test/include/dblayer/functions_mysqli.inc.php on line 893

The official fix is [Github] Piwigo commit 149f55ab but you can bypass the issue by clearing your cookie, going to /admin.php?page=plugin-TakeATour or by using an other browser the browser for just one session.
However the fix allows you to use the Duplicate filter without any issue.