Mysql: What are the diffrences between utf8_general_ci and utf8_unicode_ci?

Possible Duplicate:
What's the difference between utf8_general_ci and utf8_unicode_ci

I've got two options for unicode that look promising for a mysql database.

utf8_general_ci unicode (multilingual), case-insensitive
utf8_unicode_ci unicode (multilingual), case-insensitive

Can you please explain what is the difference between utf8_general_ci and utf8_unicode_ci? 

What are the effects of choosing one over the other when designing a database?

 Answers

utf8_general_ci is a very simple — and on Unicode, very broken — collation, 

one that gives incorrect results on general Unicode text. What it does is:

• converts to Unicode normalization form D for canonical decomposition
• removes any combining characters
• converts to upper case

This does not work correctly on Unicode, because it does not understand Unicode casing. 

Unicode casing alone is much more complicated than an ASCII-minded approach can 

handle. For example:

• The lowercase of “ẞ” is “ß”, but the uppercase of “ß” is “SS”.
• There are two lowercase Greek sigmas, but only one uppercase one; 
consider “Σίσυφος”.
• Letters like “ø” do not decompose to an “o” plus a diacritic, meaning
that it won’t correctly sort.

There are many other subtleties.

1. utf8_unicode_ci uses the standard Unicode Collation Algorithm, 
supports so called expansions and ligatures, for example: German letter ß
(U+00DF LETTER SHARP S) is sorted near "ss" Letter Π(U+0152 LATIN CAPITAL
LIGATURE OE) is sorted near "OE".

utf8_general_ci does not support expansions/ligatures, it sorts all these letters as 

single characters, and sometimes in a wrong order.

2. utf8_unicode_ci is generally more accurate for all scripts. For example, 
on Cyrillic block: utf8_unicode_ci is fine for all these languages: Russian,
Bulgarian, Belarusian, Macedonian, Serbian, and Ukrainian. While utf8_general_ci
is fine only for Russian and Bulgarian subset of Cyrillic. Extra letters used in
Belarusian, Macedonian, Serbian, and Ukrainian are sorted not well.

The cost of utf8_unicode_ci is that it is a little bit slower than utf8_general_ci.

 But that’s the price you pay for correctness. Either you can have a fast answer that’s wrong,

 or a very slightly slower answer that’s right. Your choice. It is very difficult to ever justify 

giving wrong answers, so it’s best to assume that utf8_general_ci doesn’t exist and to 

always use utf8_unicode_ci. Well, unless you want wrong answers.

Source: http://forums.mysql.com/read.php?103,187048,188748#msg-188748