Wikipedia:Double redirects
From Wikipedia, the free encyclopedia
A redirect is a special page that automatically causes the text of another page to be displayed in its place. A redirect that points to another redirect is called a double redirect. These pages are undesirable, since Wikipedia's MediaWiki software will not follow the second redirect, in order to prevent infinite loops. These situations create slow, unpleasant experiences for the reader, waste server resources, and make the navigational structure of the site confusing.
Double redirects are usually created after a move when old redirects are left unchanged and pointing towards an old name.
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[edit] How to fix a double redirect
- Suppose page title A redirects to B which in turn redirects to C.
- Follow a link to A. You will see a page containing: (a) the page title B; (b) a large link to C; (c) a very small notice in the corner saying "redirected from A".
- Click the "A" in "redirected from A".
- You will see a page containing: (a) the page title A; (b) a large link to B.
- Click "Edit this page" and change B to C.
[edit] Why do double redirects exist?
Most of the time, double redirects come about because a page is moved from one title to another, and then again to a third title. The second move will be unaware of the first and leave the first page title redirecting to the second, even though the page is now located at the third.
[edit] Lists
Current list:
- Special:DoubleRedirects - note that updates have been disabled as of January 3, 2007[1]
- alternate link showing 1000 entries: Special:DoubleRedirects&limit=1000
Old lists:
- Wikipedia:Computer help desk#Cleanup_projects
- Werdnabot can fix double-redirects when requested to. To do so, please leave a note on User:Werdnabot/Double-redirect bypass requests
[edit] Checking for double redirects
Suppose you want to check whether there are any double redirects to page C. Go to page C and click "What links here". Double (or multiple) redirects are those pages which appear in the list with both of these properties:
- Indented at least one level in comparison to the page at the top of the list, AND
- Labelled "(redirect page)".
Note that if you've just moved page C, then there might be only one page which is not indented, (the page at the top of the list), and everything else might be indented at least one level.
Once all double redirects have been fixed, the "What links here" page will have only three types of pages listed:
- Direct links from ordinary pages (not indented, not labelled "(redirect page)").
- Direct links from redirect pages (not indented; labelled "(redirect page)").
- Indirect links from ordinary pages (indented one level, not labelled "(redirect page)").
The third category does not need to be fixed -- see Wikipedia:Redirect#Don't fix links to redirects that aren't broken.
[edit] Old Topbanana method
The Topbanana method to generate a double redirect report from a Link Analysis Database is to use the following SQL:
SELECT concat( '*[http://en.wikipedia.org/w/wiki.phtml?title=', a1.art_title, '&action=edit ', a1.art_title, '] → ', replace( a2.art_title, '_', ' ') , ' → ', replace( a3.art_title, '_', ' ' ) ) FROM art a1 JOIN good_links l1 ON a1.art_id = l1.from_id JOIN art a2 ON l1.to_id = a2.art_id JOIN good_links l2 ON a2.art_id = l2.from_id JOIN art a3 ON l2.to_id = a3.art_id WHERE a1.art_is_redirect = 1 AND a2.art_is_redirect = 1 AND a3.art_is_redirect = 0 ORDER by a1.art_title;
...and then split into subsections by hand.
The Byrial method builds on this code.
