Rechercher dans le manuel MySQL

10.8.6 Examples of the Effect of Collation

Contents

Example 1: Sorting German Umlauts

Suppose that column X in table T has these latin1 column values: 

Muffler
Müller
MX Systems
MySQL

Suppose also that the column values are retrieved using the following statement:

  1. SELECT X FROM T ORDER BY X COLLATE collation_name;

The following table shows the resulting order of the values if we use ORDER BY with different collations.

latin1_swedish_ci latin1_german1_ci latin1_german2_ci
Muffler Muffler Müller
MX Systems Müller Muffler
Müller MX Systems MX Systems
MySQL MySQL MySQL

The character that causes the different sort orders in this example is the U with two dots over it (ü), which the Germans call “U-umlaut.”

  • The first column shows the result of the SELECT using the Swedish/Finnish collating rule, which says that U-umlaut sorts with Y.

  • The second column shows the result of the SELECT using the German DIN-1 rule, which says that U-umlaut sorts with U.

  • The third column shows the result of the SELECT using the German DIN-2 rule, which says that U-umlaut sorts with UE.

Example 2: Searching for German Umlauts

Suppose that you have three tables that differ only by the character set and collation used:

  1. mysql> SET NAMES utf8;
  2. mysql> CREATE TABLE german1 (
  3.          c CHAR(10)
  4.        ) CHARACTER SET latin1 COLLATE latin1_german1_ci;
  5. mysql> CREATE TABLE german2 (
  6.          c CHAR(10)
  7.        ) CHARACTER SET latin1 COLLATE latin1_german2_ci;
  8. mysql> CREATE TABLE germanutf8 (
  9.          c CHAR(10)
  10.        ) CHARACTER SET utf8 COLLATE utf8_unicode_ci;

Each table contains two records:

  1. mysql> INSERT INTO german1 VALUES ('Bar'), ('Bär');
  2. mysql> INSERT INTO german2 VALUES ('Bar'), ('Bär');
  3. mysql> INSERT INTO germanutf8 VALUES ('Bar'), ('Bär');

Two of the above collations have an A = Ä equality, and one has no such equality (latin1_german2_ci). For that reason, you'll get these results in comparisons:

  1. mysql> SELECT * FROM german1 WHERE c = 'Bär';
  2. +------+
  3. | c    |
  4. +------+
  5. | Bar  |
  6. | Bär  |
  7. +------+
  8. mysql> SELECT * FROM german2 WHERE c = 'Bär';
  9. +------+
  10. | c    |
  11. +------+
  12. | Bär  |
  13. +------+
  14. mysql> SELECT * FROM germanutf8 WHERE c = 'Bär';
  15. +------+
  16. | c    |
  17. +------+
  18. | Bar  |
  19. | Bär  |
  20. +------+

This is not a bug but rather a consequence of the sorting properties of latin1_german1_ci and utf8_unicode_ci (the sorting shown is done according to the German DIN 5007 standard).


Find a PHP function

Document created the 26/06/2006, last modified the 26/10/2018
Source of the printed document:https://www.gaudry.be/en/mysql-rf-charset-collation-effect.html

The infobrol is a personal site whose content is my sole responsibility. The text is available under CreativeCommons license (BY-NC-SA). More info on the terms of use and the author.

References

  1. View the html document Language of the document:en Manuel MySQL : https://dev.mysql.com/

These references and links indicate documents consulted during the writing of this page, or which may provide additional information, but the authors of these sources can not be held responsible for the content of this page.
The author This site is solely responsible for the way in which the various concepts, and the freedoms that are taken with the reference works, are presented here. Remember that you must cross multiple source information to reduce the risk of errors.

Contents Haut