This setting is sent by the browser at every request to the server as ‘Accept-Language’ header and can look like this “pl,en-us;q=0.7,en;q=0.3″. You can check it with Live HTTP Headers Add-on for Firefox and read more about this header at W3C HTTP specification.

In PHP I could do it by checking the value of $_SERVER['HTTP_ACCEPT_LANGUAGE'] and issuing the header(”Location: /LANG/foo.php”,TRUE,301); command.

But I didn’t want to use PHP and did want to do it with .htaccess and mod rewrite. The first thought was to use RewriteCond %{HTTP_ACCEPT_LANGUAGE} as the analogy to RewriteCond %{HTTP_USER_AGENT} or RewriteCond %{HTTP_REFERER}. Unfortunately RewriteCond %{HTTP_ACCEPT_LANGUAGE} does not work! This variable is not present.

What is the solution? Looking more closely at the documentation at http://httpd.apache.org/docs/2.2/mod/mod_rewrite.html we have:

%{HTTP:header}, where header can be any HTTP MIME-header name, can always be used to obtain the value of a header sent in the HTTP request.

Which means we can obtain the value of default language setting of the browser by using RewriteCond %{HTTP:Accept-Language}. This is the simple solution, difficult to find on the web.

So if we have a website with three languages: English, German and Spanish and we want English to be the default we would use for example this in .htaccess:

#The 'Accept-Language' header starts with 'de'
#and the test is case-insensitive ([NC])
RewriteCond %{HTTP:Accept-Language} ^de [NC]
#Redirect user to /de/hauptseite address
#sending 301 (Moved Permanently) HTTP status code
RewriteRule ^$ /de/hauptseite [L,R=301]

RewriteCond %{HTTP:Accept-Language} ^es [NC]
RewriteRule ^$ /es/pagina-primera [L,R=301]

#For every other language (including English :)) use English
RewriteRule ^$ /en/main-page [L,R=301]

If you need to be more specific (eg. redirect accordingly to US or Great Britain English (en-us and en-gb)) you would not check only the first two signs of ‘Accept-Language’ header but you would need to prepare a little bit more complicated regular expression (some language settings are only two signs, some five signs).

I also thought about possibility of changing redirection addresses from within the CMS system (so that the admin can change main-page, hauptseite or pagina-primera to whatever he/she wishes). The best way would be to save this information in another file (e.g. lang-redirects.conf) and include it within .htaccess. Unfortunately config files inclusion is not possible in .htaccess scope. Another solution I thought about was using mapping-function but it doesn’t work, either.
So the only we can do is to edit .htaccess itself. If anyone knows a nicer solution  please share it with us.

Do you know any other tips & tricks regarding .htaccess and/or mod rewrite? We are waiting.

You can say – where is the problem? Let’s sum everything together and divide by the number of items.

Yes, but I wanted that in my voting system you don’t have to rank all the elements, e.g. let’s presume we have: cuisine, music and appearance. If someone wants to give a rank for music it is not obligatory to rank cuisine and appearance.

That’s why I had to use NULL values in my table. I came up with this structure:

DROP TABLE IF EXISTS `voting`;

CREATE TABLE IF NOT EXISTS `voting` (
`opinion_id` mediumint(9)
unsigned NOT NULL auto_increment,
`rank_0` tinyint(4) default NULL,
`rank_1` tinyint(4) default NULL,
`rank_2` tinyint(4) default NULL,
PRIMARY KEY  (`opinion_id`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1
COLLATE=latin1_general_ci;

And let’s insert these values:

INSERT INTO `voting` VALUES (1, 1, 2, NULL);
INSERT INTO `voting` VALUES (2, 3, NULL, 4);
INSERT INTO `voting` VALUES (3, 3, 1, 2);

When we do:

SELECT *, (V.rank_0 + V.rank_1 + V.rank_2) / 3
AS row_avg FROM voting V

we only receive correct averages for the rows where all values are not NULL. But when I have e.g. 3, NULL, 4 I’d like to get 3.5 as a return. That’s the moment when function COALESCE() comes handy.

What does COALESCE () do? From MySQL manual we have:

Returns the first non-NULL value in the list, or NULL if there are no non-NULL values.

mysql> SELECT COALESCE(NULL,1);
-> 1
mysql> SELECT COALESCE(NULL,NULL,NULL);
-> NULL

And these information will help us to build another SELECT statement:

SELECT *,

#first part
(COALESCE(V.rank_0, 0)
+ COALESCE(V.rank_1, 0)
+ COALESCE(V.rank_2, 0))
/

#second part
(3 -
(COALESCE(V.rank_0 - V.rank_0, 1)
+ COALESCE(V.rank_1 - V.rank_1, 1)
+ COALESCE(V.rank_2 - V.rank_2, 1))
) AS row_avg FROM voting V

And now we have the average returned just as we wanted. NULLs are not taken into account when we do the calculations.

So what is inside this SELECT statement? COALESCE() returns the first non-NULL value so in the first part COALESCE(V.rank_0, 0) would return 0 if rank_0 is NULL or rank_0 itself if it is not NULL. The whole first part of SELECT would give us the sum of non-NULL values in the row.

In the second part we have (COALESCE(V.rank_0 – V.rank_0, 1) which would return 1 only if rank_0 is NULL (rank_0 – rank_0 is still NULL). We would receive 0 if rank_0 is not NULL (e.g. 4 – 4 = 0 and it is first non-NULL value in the list to be returned). So the second part let’s us count the number of columns which have NULL values and subtract it from the number of all items.

This way we have our average from row in MySQL database :)

Do you know any other useful things we can do with COALESCE function or averages in general? Please share them with us.

I hope you would also find here some useful PHP / MySQL tips and tricks for you as I find them on other websites, forums and blogs. In my posts I try to be as accurate and concise as possible. Always waiting for your comments and sharing your experience.

Enjoy!

Michal Borychowski