What is the difference between “utf8_unicode_ci” a

I recently upgraded WAMPServer and now in phpMyAdmin, I see both collations utf8_unicode_ci and utf8_unicode_520_ci. I was using "utf8_unicode_ci" for Turkish applications, but I wonder what is different in the new *_520 collation?

回答1:

As documented under Collation Names:

Unicode collation names may include a version number to indicate the version of the Unicode Collation Algorithm (UCA) on which the collation is based. UCA-based collations without a version number in the name use the version-4.0.0 UCA weight keys: http://www.unicode.org/Public/UCA/4.0.0/allkeys-4.0.0.txt. A collation name such as utf8_unicode_520_ci is based on UCA 5.2.0 weight keys: http://www.unicode.org/Public/UCA/5.2.0/allkeys.txt.

回答2:

As you can read here (thanks user3399549 for link) there is problem with sorting/comparing polish letter "Ł" (L with stroke) (lower case: "ł"; html esc: ł and Ł ) here Peter Gulutzan explain differences between collocations:

We have these collations and rules for Ł :

utf8_polish_ci      Ł greater than L and less than M
utf8_unicode_ci     Ł greater than L and less than M
utf8_unicode_520_ci Ł equal to L
utf8_general_ci     Ł greater than Z

In polish language letter Ł is after letter L and before M. We can write this in following way (for clarify):

L < Ł < M 

and 

L != Ł

So to avoid this kind of problems (with sorting/comapring) use utf8_unicode_ci.

回答3:

If you want only Turkish, then consider utf8_turkish_ci. Here are most of the differences (taken from http://mysql.rjweb.org/utf8_collations.html ):

utf8 : utf8_turkish_ci             A=a=ª=À=Á=Á=Â=Ã=Ä=Å=à=á=á=â=ã=ä=å=Ā=ā=Ą=ą  Aa  ae          az       Æ=æ
utf8 : utf8_unicode_520_ci         A=a=ª=À=Á=Á=Â=Ã=Ä=Å=à=á=á=â=ã=ä=å=Ā=ā=Ą=ą  Aa  ae=Æ=æ      az
utf8 : utf8_unicode_ci             A=a=ª=À=Á=Á=Â=Ã=Ä=Å=à=á=á=â=ã=ä=å=Ā=ā=Ą=ą  Aa  ae          az       Æ=æ

utf8 : utf8_turkish_ci             B=b  C=c=Č=č          ch  cz  Ç=ç  D=d=Ď=ď      dz  Ð=ð
utf8 : utf8_unicode_520_ci         B=b  C=c=Ç=ç=Č=č      ch  cz       D=d=Ð=ð=Ď=ď  dz
utf8 : utf8_unicode_ci             B=b  C=c=Ç=ç=Č=č      ch  cz       D=d=Ď=ď      dz  Ð=ð

utf8 : utf8_turkish_ci             F=f  fz  ƒ  G=g=Ģ=ģ      gz  Ğ=ğ  H=h  hz
utf8 : utf8_unicode_520_ci         F=f  fz  ƒ  G=g=Ğ=ğ=Ģ=ģ  gz       H=h  hz
utf8 : utf8_unicode_ci             F=f  fz  ƒ  G=g=Ğ=ğ=Ģ=ģ  gz       H=h  hz

utf8 : utf8_turkish_ci             I=ı  i=Ì=Í=Í=Î=Ï=ì=í=í=î=ï=Ī=ī=Į=į=İ   ij=ĳ   iz              J=j
utf8 : utf8_unicode_520_ci         I=i=Ì=Í=Í=Î=Ï=ì=í=í=î=ï=Ī=ī=Į=į=İ      ij=ĳ   iz           ı  J=j
utf8 : utf8_unicode_ci             I=i=Ì=Í=Í=Î=Ï=ì=í=í=î=ï=Ī=ī=Į=į=İ      ij=ĳ   iz           ı  J=j

utf8 : utf8_turkish_ci             K=k=Ķ=ķ   L=l=Ĺ=ĺ=Ļ=ļ          lj=Ǉ=ǈ=ǉ      ll  lz  Ł=ł  M=m  N=n=Ñ=ñ=Ń=ń=Ņ=ņ=Ň=ň  nz
utf8 : utf8_unicode_520_ci         K=k=Ķ=ķ   L=l=Ĺ=ĺ=Ļ=ļ=Ł=ł      lj=Ǉ=ǈ=ǉ      ll  lz       M=m  N=n=Ñ=ñ=Ń=ń=Ņ=ņ=Ň=ň  nz
utf8 : utf8_unicode_ci             K=k=Ķ=ķ   L=l=Ĺ=ĺ=Ļ=ļ          lj=Ǉ=ǈ=ǉ      ll  lz  Ł=ł  M=m  N=n=Ñ=ñ=Ń=ń=Ņ=ņ=Ň=ň  nz

utf8 : utf8_turkish_ci             O=o=º=Ò=Ó=Ó=Ô=Õ=ò=ó=ó=ô=õ          oe=Œ=œ      oz  Ö=ö      Ø=ø
utf8 : utf8_unicode_520_ci         O=o=º=Ò=Ó=Ó=Ô=Õ=Ö=Ø=ò=ó=ó=ô=õ=ö=ø  oe=Œ=œ      oz
utf8 : utf8_unicode_ci             O=o=º=Ò=Ó=Ó=Ô=Õ=Ö=ò=ó=ó=ô=õ=ö      oe=Œ=œ      oz           Ø=ø

utf8 : utf8_turkish_ci             P=p  Q=q  R=r=Ř=ř   S=s=Š=Š=š=š        sh  ss=ß  sz  Ş=ş
utf8 : utf8_unicode_520_ci         P=p  Q=q  R=r=Ř=ř   S=s=Ş=ş=Š=Š=š=š    sh  ss=ß  sz
utf8 : utf8_unicode_ci             P=p  Q=q  R=r=Ř=ř   S=s=Ş=ş=Š=Š=š=š    sh  ss=ß  sz

utf8 : utf8_turkish_ci             T=t=Ť=ť  TM=tm=™  tz  U=u=Ù=Ú=Ú=Û=ù=ú=ú=û=Ū=ū=Ů=ů=Ų=ų      ue      uz  Ü=ü      V=v
utf8 : utf8_unicode_520_ci         T=t=Ť=ť  TM=tm=™  tz  U=u=Ù=Ú=Ú=Û=Ü=ù=ú=ú=û=ü=Ū=ū=Ů=ů=Ų=ų  ue      uz           V=v
utf8 : utf8_unicode_ci             T=t=Ť=ť  TM=tm=™  tz  U=u=Ù=Ú=Ú=Û=Ü=ù=ú=ú=û=ü=Ū=ū=Ů=ů=Ų=ų  ue      uz           V=v

utf8 : utf8_turkish_ci             W=w  X=x  Y=y=Ý=Ý=ý=ý=ÿ=Ÿ      yz
utf8 : utf8_unicode_520_ci         W=w  X=x  Y=y=Ý=Ý=ý=ý=ÿ=Ÿ      yz
utf8 : utf8_unicode_ci             W=w  X=x  Y=y=Ý=Ý=ý=ý=ÿ=Ÿ      yz

utf8 : utf8_turkish_ci             Z=z=Ž=Ž=ž=ž  zh  zz           Þ=þ
utf8 : utf8_unicode_520_ci         Z=z=Ž=Ž=ž=ž  zh  zz           Þ=þ
utf8 : utf8_unicode_ci             Z=z=Ž=Ž=ž=ž  zh  zz           Þ=þ

Notice how Æ, Ç, Ð, Ğ, etc, are sorted differently in the different collations.

520 probably will not impact normal text, especially just Turkish. For example, Turkish and 520 consider Ð to be a separate letter, but utf8_unicode_ci treats it equal to D. It looks like 520 is 'closer' to turkish, but not identical for all the letters.