Oracle 5.0, Справочное руководство

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Collation Issues
786
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:
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:
mysql> SET NAMES utf8;
mysql> CREATE TABLE german1 (
-> c CHAR(10)
-> ) CHARACTER SET latin1 COLLATE latin1_german1_ci;
mysql> CREATE TABLE german2 (
-> c CHAR(10)
-> ) CHARACTER SET latin1 COLLATE latin1_german2_ci;
mysql> CREATE TABLE germanutf8 (
-> c CHAR(10)
-> ) CHARACTER SET utf8 COLLATE utf8_unicode_ci;
Each table contains two records:
mysql> INSERT INTO german1 VALUES ('Bar'), ('Bär');
mysql> INSERT INTO german2 VALUES ('Bar'), ('Bär');
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:
mysql> SELECT * FROM german1 WHERE c = 'Bär';
+------+
| c |
+------+
| Bar |
| Bär |
+------+
mysql> SELECT * FROM german2 WHERE c = 'Bär';
+------+
| c |
+------+