Cut Final Character

SQL

USE dewiktionary_p;

SELECT 
p1.page_title,
p1.page_id,
p1.page_namespace,
c1.cl_from,
c1.cl_to,
# As soon as I include one of the following fields,
# the query does not finish within 5 minutes,
# reason unclear.
#p2.page_title,
#p2.page_id,
#p2.page_namespace,
#c2.cl_from,
#c2.cl_to,
'Dummy'
FROM page p1
JOIN categorylinks c1
ON  c1.cl_from = p1.page_id
and c1.cl_to = 'Grundformeintrag_(Deutsch)'
join page p2
on  p2.page_namespace = 0
and p2.page_is_redirect = 0
#The following will make the query very slow (about 600 seconds):
#and p2.page_title in(concat(lower(left(p1.page_title,1)), mid(p1.page_title, 2, length(p1.page_title)-2)),
#                     concat(upper(left(p1.page_title,1)), mid(p1.page_title, 2, length(p1.page_title)-2)))
and p2.page_title = left(p1.page_title, length(p1.page_title)-1)
JOIN categorylinks c2
ON  c2.cl_from = p2.page_id
and c2.cl_to = 'Grundformeintrag_(Deutsch)'
where p1.page_namespace = 0
AND p1.page_is_redirect = 0
AND p1.page_title REGEXP '^[[:alpha:]]{3,30}f$';
SQL

Checking query status...
