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How to add a collation
Alexander Barkov
September, 2007
MySQL AB
Copyright 2007 MySQL AB
The World’s Most Popular Open Source Database
1
Plan for this session
•
•
•
•
What is collation?
The WEIGHT_STRING function
Types of collations in MySQL
Adding collations for 8-bit character sets without
recompiling
• Adding collations for Unicode character sets without
recompiling
• Adding collations into the source code
Copyright 2007 MySQL AB
The World’s Most Popular Open Source Database
2
What is collation?
• Collation is a set of rules how to compare and sort
character strings.
• Every MySQL collation belongs to a single character
set.
• Every MySQL character set can have one or more
collations which belong to it.
• This session assumes that the character sets already
exist ("How to add a new character set" would be another session).
Copyright 2007 MySQL AB
The World’s Most Popular Open Source Database
3
The WEIGHT_STRING SQL function
New function in 5.2:
WEIGHT_STRING(character_string_expression) -> binary_key
Converts a character string into its binary key,
which is used for comparison and sorting. Any two strings which are
equal in their collation return the same results:
SELECT WEIGHT_STRING('a'); -> 0x41
SELECT WEIGHT_STRING('A'); -> 0x41
On the main goals of WEIGHT_STRING: to make debugging and testing
of collations easier.
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The World’s Most Popular Open Source Database
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Types of MySQL collations:
•
•
•
•
•
Collations for 8-bit character sets.
Collations for non-Unicode multi-byte character sets.
Collations for Unicode character sets.
xxx_bin collations
Other collations (minority)
Copyright 2007 MySQL AB
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"Simple" collations for 8-bit character sets.
Internal implementation uses an array of 256 weights, with
one-to-one mapping between a character and its weight.
mysql> create table t1 (c1 varchar(2) character set latin1
collate latin1_swedish_ci);
Query OK, 0 rows affected (0.10 sec)
mysql> insert into t1 values ('a'),('A');
Query OK, 2 rows affected (0.00 sec)
Records: 2 Duplicates: 0 Warnings: 0
mysql> select c1, hex(weight_string(c1)) from t1;
+------+------------------------+
| c1
| hex(weight_string(c1)) |
+------+------------------------+
| a
| 41
|
| A
| 41
|
+------+------------------------+
2 rows in set (0.00 sec)
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The World’s Most Popular Open Source Database
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Collations for non-Unicode multi-byte character sets: type #1
•
ASCII range: one-to-one mapping from code to weight, case insensitive
•
Multi-byte characters: weight = code
Example: sjis_japanese_ci:
mysql> create table t1 (c1 varchar(2) character set sjis collate utf8_japanese_ci);
Query OK, 0 rows affected (0.07 sec)
mysql> insert into t1 values ('a'),('A'),(0x82C0);
Query OK, 3 rows affected (0.00 sec)
Records: 3
Duplicates: 0
Warnings: 0
mysql> select c1, hex(weight_string(c1)) from t1;
+------+------------------------+
| c1
| hex(weight_string(c1)) |
+------+------------------------+
| a
| 41
|
| A
| 41
|
| ぢ
| 82C0
|
+------+------------------------+
3 rows in set (0.00 sec)
Copyright 2007 MySQL AB
The World’s Most Popular Open Source Database
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Collations for non-Unicode multi-byte character sets: type #2
•
ASCII range: one-to-one mapping from code to weight, case insensitive
•
Multi-byte characters: one-to-one mapping from code to weight
Example: gbk_chinese_ci:
mysql> create table t1 (c1 varchar(2) character set gbk collate
gbk_chinese_ci);
Query OK, 0 rows affected (0.02 sec)
mysql> insert into t1 values ('a'),('A'),(0x81B0),(0x81B1);
Query OK, 4 rows affected (0.01 sec)
Records: 4 Duplicates: 0 Warnings: 0
mysql> select c1, hex(c1), hex(weight_string(c1)) from t1;
+------+---------+------------------------+
| c1
| hex(c1) | hex(weight_string(c1)) |
+------+---------+------------------------+
| a
| 61
| 41
|
| A
| 41
| 41
|
| 伆
| 81B0
| C286
|
| 伇
| 81B1
| CACC
|
+------+---------+------------------------+
4 rows in set (0.00 sec)
Copyright 2007 MySQL AB
The World’s Most Popular Open Source Database
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Collations for Unicode multi-byte character sets: type #1
•
One-to-one mapping from code to weight, case insensitive
•
Removes accents before converting from code to weight
Example: utf8_general_ci:
mysql> create table t1 (c1 char(1) character set utf8 collate
utf8_general_ci);
Query OK, 0 rows affected (0.11 sec)
mysql> insert into t1 values ('a'),('A'),('À'), ('á');
Query OK, 0 rows affected (0.06 sec)
Query OK, 4 rows affected (0.00 sec)
Records: 4 Duplicates: 0 Warnings: 0
mysql> select c1, hex(c1), hex(weight_string(c1)) from t1;
+------+---------+------------------------+
| c1
| hex(c1) | hex(weight_string(c1)) |
+------+---------+------------------------+
| a
| 61
| 0041
|
| A
| 41
| 0041
|
| À
| C380
| 0041
|
| á
| C3A1
| 0041
|
+------+---------+------------------------+
4 rows in set (0.20 sec)
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Collations for the Unicode character sets: type#2,
based on "Unicode collation algorithm" (UCA).
• One weight uses 2 bytes
• One-character-to-zero-weights: ignorable: "U+0000
NULL" does't have a weight (or has an empty weight)
• One-character-to-one-weight
• One-character-to-many-weights: expansion: German
letter ß (SZ LEAGUE, or SHARP S)
• Many-characters-to-one-weight: contraction: "ch" is a
separate single letter in Czech
• Many-characters-to-many-weights: contraction with
expansion: not supported
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Weights in a UCA collation
mysql> create table t1 (c1 varchar(2) character set utf8 collate utf8_czech_ci);
Query OK, 0 rows affected (0.00 sec)
mysql> insert into t1 values (0x00),('a'),('A'),('h'),('i'),('s'),('ss'),('ß'),('ch');
Query OK, 9 rows affected (0.00 sec)
Records: 9
Duplicates: 0
Warnings: 0
mysql> select c1, hex(c1), hex(weight_string(c1)) from t1 order by c1;
+------+---------+------------------------+
| c1
| hex(c1) | hex(weight_string(c1)) |
+------+---------+------------------------+
|
| 00
|
| <- ignorable
| a
| 61
| 0E33
|
| A
| 41
| 0E33
|
| h
| 68
| 0EE1
|
| ch
| 6368
| 0EE2
|
| i
| 69
| 0EFB
|
| s
| 73
| 0FEA
|
| ss
| 7373
| 0FEA0FEA
|
| ß
| C39F
| 0FEA0FEA
| <- expansion
<- contraction
+------+---------+------------------------+
9 rows in set (0.00 sec)
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Collations that can be added without
recompiling
• “Simple” collations for 8-bit character sets.
• UCA-based collations for Unicode character sets.
• xxx_bin
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Adding a collation: choosing an ID
First step: find a vacant ID (IDs are used in .frm, binlog, protocol, etc)
mysql> select id from information_schema.collations order by id ;
+-----+
| id
|
+-----+
|
1 |
...
|
55 |
|
57 | <- 56
|
58 |
...
| 242 |
| 243 |
| 254 | <- 244-253
+-----+
196 rows in set (0.02 sec)
Copyright 2007 MySQL AB
The World’s Most Popular Open Source Database
13
Adding a simple collation for an 8-bit character
set
Step 1: Declare name-to-id association in
/usr/share/mysql/charsets/Index.xml:
<charset name="latin1">
...
<collation name="latin1_test_ci" id="56"/>
...
</charset>
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The World’s Most Popular Open Source Database
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Adding a simple collation for an 8-bit character
set
Step 2: Define code-to-weight mapping table in
/usr/share/mysql/charsets/latin1.xml:
<collation name="latin1_test_ci">
<map>
00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
10 11 12 13 14 15 16 17 18 19 1A 1B 1C 1D 1E 1F
20 21 22 23 24 25 26 27 28 29 2A 2B 2C 2D 2E 2F
30 31 32 33 34 35 36 37 38 39 3A 3B 3C 3D 3E 3F
40 41 42 43 44 45 46 47 48 49 4A 4B 4C 4D 4E 4F
50 51 52 53 54 55 56 57 58 59 5A 5B 5C 5D 5E 5F
60 41 42 43 44 45 46 47 48 49 4A 4B 4C 4D 4E 4F
50 51 52 53 54 55 56 57 58 59 5A 7B 7C 7D 7E 7F
80 81 82 83 84 85 86 87 88 89 8A 8B 8C 8D 8E 8F
90 91 92 93 94 95 96 97 98 99 9A 9B 9C 9D 9E 9F
A0 A1 A2 A3 A4 A5 A6 A7 A8 A9 AA AB AC AD AE AF
B0 B1 B2 B3 B4 B5 B6 B7 B8 B9 BA BB BC BD BE BF
41 41 41 41 5B 5D 5B 43 45 45 45 45 49 49 49 49
44 4E 4F 4F 4F 4F 5C D7 5C 55 55 55 59 59 DE DF
41 41 41 41 5B 5D 5B 43 45 45 45 45 49 49 49 49
44 4E 4F 4F 4F 4F 5C F7 5C 55 55 55 59 59 DE FF
</map>
</collation>
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Adding a UCA collation: supported character
sets
UCA collations can be added for the following character
sets, without recompiling "mysqld" sources:
• MySQL 4.1, 5.0, 5.1: utf8 and ucs2
• MySQL 5.2.x will also support utf16 and utf32
(the patch is currently in review)
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Adding a UCA-based collation
• A collation is added with help of subset of "Locale Data
Markup Language" (LDML) http://unicode.org/reports/tr35/
• MySQL supports LDML starting from versions: 5.0.46,
5.1.20, 5.2.6
• A new UCA collation uses utf8_unicode_ci as a base (or
ucs2_unicde_ci, in case if ucs2)
• Collation ordering rules do not define the whole collation,
but instead describe only how a collation differs from
utf8_unicode_ci
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Adding a UCA-based collation: editing
Index.xml
Collation ordering rules are to be put between
<rules>...</rules> tags of character set definition file
/usr/share/mysql/charsets/Index.xml
<charset name="utf8">
...
<!-- associate collation name with its ID -->
<collation name="utf8_phone_ci" id="252">
<rules>
... put rules here...
</rules>
</collation>
...
</charset>
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The World’s Most Popular Open Source Database
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LDML ordering rule types
• Reset rules
• Shift rules:
– Shift rules defining primary difference
– Shift rules defining secondary difference
– Shift rules defining tertiary difference
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LDML: reset rules
<reset>A</reset>
or
<reset>\u0041</reset>
Reset rules do not change the order of the character itself ("A" in this example), but
tell that the characters given in subsequent shift rules will be sorted near the letter "A".
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LDML: shift rules: primary difference
<p>G<p>
or
<p>\u0047</p>
Reset+Shift example:
<reset>A</reset>
<p>G</p>
says that "G" will be greater than "A", but less than "B".
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Shift rules: Secondary and tertiary difference
Secondary difference:
<s>G</s>
or
<s>\u0047</s>
Tertiary difference:
<t>G</t>
or
<t>\u0047</t>
Shift+Reset example (Swedish):
<reset>Y</reset>
<s>\u00DC</s>
<t>\u00FC</t>
Defines this sorting order: YyÜü
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Secondary and tertiary difference
However, currently MySQL does not support secondary and tertiary
difference yet. So these rules actually make all these four letters
equal to each other (not only for comparison, but for sorting as well),
thus mutual order of these letters (YyÜü) in ORDER BY is not strict.
Support for secondary and tertiary levels is on TODO (WL#896).
Which difference to use:
- Secondary - for accent
- Tertiary - for case
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Pre-defined UCA collations: utf8_unicode_ci
In utf8_unicode_ci, accented letters are equal to thei r non-accented counterparts.
mysql> create table t1 (a char(1) character set utf8 collate utf8_unicode_ci);
Query OK, 0 rows affected (0.24 sec)
mysql> insert into t1 values ('C'),('Č'),('S'),('Š'),('Z'),('Ž'),('N'),('Ñ');
Query OK, 8 rows affected (0.01 sec)
Records: 8
Duplicates: 0
Warnings: 0
mysql> select group_concat(a) from t1 group by a;
+-----------------+
| group_concat(a) |
+-----------------+
| C,Č
|
| N,Ñ
|
| S,Š
|
| Z,Ž
|
+-----------------+
4 rows in set (0.05 sec)
Some languages consider certain accented characters as separate letters. MySQL provides
predefined collations for a number of languages.
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Predefined UCA collations: utf8_slovenian_ci
utf8_slovenian_ci changes ordering of the letters Č, Š and Ž, making them separate
letters.
LDML definition, equivalent to utf8_slovenian_ci ordering would be:
<rules>
<reset>C</reset><p>\u010C</p><t>\u010D</t>
<reset>S</reset><p>\u0160</p><t>\u0161</t>
<reset>Z</reset><p>\u017D</p><t>\u017E</t>
</rules>
Note: Index.xml does not really have a definition for utf8_slovenian_ci.
It is defined in strings/ctype-uca.c
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Predefined UCA collations: utf8_slovenian_ci
Usage example:
mysql> create table t1 (a char(1) character set utf8 collate utf8_slovenian_ci);
Query OK, 0 rows affected (0.11 sec)
mysql> insert into t1 values ('C'),('Č'),('S'),('Š'),('Z'),('Ž'),('N'),('Ñ');
Query OK, 8 rows affected (0.00 sec)
Records: 8
Duplicates: 0
Warnings: 0
mysql> select group_concat(a) from t1 group by a;
+-----------------+
| group_concat(a) |
+-----------------+
| C
|
| Č
|
| N,Ñ
|
| S
|
| Š
|
| Z
|
| Ž
|
+-----------------+
7 rows in set (0.02 sec)
Note: Ñ is still equal to its non-accented counterpart.
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Predefined UCA collations: utf8_spanish_ci
utf8_spanish_ci changes ordering of the letter Ñ,
making it separate letter.
LDML definition, equivalent to utf8_spanish_ci ordering:
<rules>
<reset>N</reset><p>\u00D1</p><s>\u00F1</s>
</rules>
Note: Index.xml does not really have a definition for utf8_spanish_ci.
It is defined in strings/ctype-uca.c
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Predefined UCA collations: utf8_spanish_ci
Usage example:
mysql> create table t1 (a char(1) character set utf8 collate utf8_spanish_ci);
mysql> insert into t1 values ('C'),('Č'),('S'),('Š'),('Z'),('Ž'),('N'),('Ñ');
Query OK, 8 rows affected (0.00 sec)
Records: 8
Duplicates: 0
Warnings: 0
mysql> select group_concat(a) from t1 group by a;
+-----------------+
| group_concat(a) |
+-----------------+
| C,Č
|
| N
|
| Ñ
|
| S,Š
|
| Z,Ž
|
+-----------------+
5 rows in set (0.00 sec)
Note: letters Č, Š, Ž are still equal to their non-accented counterparts.
Copyright 2007 MySQL AB
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Adding a UCA collation: Slovenian + Spanish together
What if I need two languages at the same time? Combine the rules and put them into Index.xml!
1. Edit Index.xml and put the rules inside "utf8" definition:
<charset name="utf8">
...
<collation name="utf8_spanishslovenian_ci" id="251">
<rules>
<reset>C</reset><p>\u010C</p><t>\u010D</t>
<reset>N</reset><p>\u00D1</p><s>\u00F1</s>
<reset>S</reset><p>\u0160</p><t>\u0161</t>
<reset>Z</reset><p>\u017D</p><t>\u017E</t>
</rules>
</collation>
...
</charset>
2. Restart mysqld
3. Check that mysqld detected the new collation:
mysql> show collation like '%spanishslovenian%';
+--------------------------+---------+-----+---------+----------+---------+
| Collation
| Charset | Id
| Default | Compiled | Sortlen |
+--------------------------+---------+-----+---------+----------+---------+
| utf8_spanishslovenian_ci | utf8
| 251 |
|
|
8 |
+--------------------------+---------+-----+---------+----------+---------+
1 row in set (0.00 sec)
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Adding a UCA collation: testing
utf8_spanishslovenian_ci
mysql> create table t1 (a char(1) character set utf8 collate
utf8_spanishslovenian_ci);
mysql> insert into t1 values
('C'),('Č'),('S'),('Š'),('Z'),('Ž'),('N'),('Ñ');
Query OK, 8 rows affected (0.05 sec)
Records: 8
Duplicates: 0
Warnings: 0
mysql> select group_concat(a) from t1 group by a;
+-----------------+
| group_concat(a) |
+-----------------+
| C
|
| Č
|
| N
|
| Ñ
|
| S
|
| Š
|
| Z
|
| Ž
|
+-----------------+
8 rows in set (0.00 sec)
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A phone book application
Suppose we have a web application, users post their names and phone numbers.
Phone numbers can have very different format:
+7-12345-67
+7-12-345-67
+7 12 345 67
+7 (12) 345 67
+71234567
Searching for a phone number is difficult.
Solution: reorder punctuation characters, making them ignorable
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Adding utf8_phone_ci
1. Add rules to /usr/share/mysql/Index.xml:
<charset name="utf8">
...
<collation name="utf8_phone_ci" id="252">
<rules>
<reset>\u0000</reset>
<s>\u0020</s> <!-- space
-->
<s>\u0028</s> <!-- l p
-->
<s>\u0029</s> <!-- r p
-->
<s>\u002B</s> <!-- plus
-->
<s>\u002D</s> <!-- hyphen -->
</rules>
</collation>
...
</charset>
2. Restart mysqld
3. Check that mysqld detected the new collation:
mysql> show collation like '%phone%';
+---------------+---------+-----+---------+----------+---------+
| Collation
| Charset | Id
| Default | Compiled | Sortlen |
+---------------+---------+-----+---------+----------+---------+
| utf8_phone_ci | utf8
| 252 |
|
|
8 |
+---------------+---------+-----+---------+----------+---------+
1 row in set (0.04 sec)
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Testing utf8_phone_ci
mysql> create table phonebook (name varchar(64), phone varchar(64) character set
utf8 collate utf8_phone_ci);
Query OK, 0 rows affected (0.01 sec)
mysql> insert into phonebook values ('Svoj','+7 912 800 80 02');
Query OK, 1 row affected (0.05 sec)
mysql> insert into phonebook values ('Hf','+7 (912) 800 80 04');
Query OK, 1 row affected (0.00 sec)
mysql> insert into phonebook values ('Bar','+7-912-800-80-01');
Query OK, 1 row affected (0.00 sec)
mysql> insert into phonebook values ('Ramil','(7912) 800 80 03');
Query OK, 1 row affected (0.01 sec)
mysql> insert into phonebook values ('Sanja','+380 (912) 8008005');
Query OK, 1 row affected (0.02 sec)
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Testing utf8_phone_ci
mysql> select * from phonebook order by
phone;
+-------+--------------------+
| name | phone
|
+-------+--------------------+
| Sanja | +380 (912) 8008005 |
| Bar
| +7-912-800-80-01
|
| Svoj | +7 912 800 80 02
|
| Ramil | (7912) 800 80 03
|
| Hf
| +7 (912) 800 80 04 |
+-------+--------------------+
5 rows in set (0.00 sec)
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Testing utf8_phone_ci
mysql> select * from t1 where phone='+7(912)800-80-01';
+------+------------------+
| name | phone
|
+------+------------------+
| Bar | +7-912-800-80-01 |
+------+------------------+
1 row in set (0.00 sec)
mysql> select * from t1 where phone='+7(912)800-80-02';
+------+------------------+
| name | phone
|
+------+------------------+
| Svoj | +7 912 800 80 02 |
+------+------------------+
1 row in set (0.00 sec)
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Testing utf8_phone_ci
mysql> select * from t1 where phone='+7(912)800-80-03';
+-------+------------------+
| name
| phone
|
+-------+------------------+
| Ramil | (7912) 800 80 03 |
+-------+------------------+
1 row in set (0.00 sec)
mysql> select * from t1 where phone='+7(912)800-80-04';
+------+--------------------+
| name | phone
|
+------+--------------------+
| Hf
| +7 (912) 800 80 04 |
+------+--------------------+
1 row in set (0.00 sec)
mysql> select * from phonebook where phone='+380-912-800-80-05';
+-------+--------------------+
| name
| phone
|
+-------+--------------------+
| Sanja | +380 (912) 8008005 |
+-------+--------------------+
1 row in set (0.00 sec)
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Adding a built-in collation
A conglomerate object representing a
character set + collation pair:
typedef struct charset_info_st
{
uint
number;
uint
primary_number;
uint
binary_number;
uint
state;
const char *csname;
const char *name;
const char *comment;
const char *tailoring;
uchar
*ctype;
uchar
*to_lower;
uchar
*to_upper;
uchar
*sort_order;
uint16
*contractions;
uint16
**sort_order_big;
uint16
*tab_to_uni;
MY_UNI_IDX
*tab_from_uni;
uchar
*state_map;
uchar
*ident_map;
uint
strxfrm_multiply;
uchar
caseup_multiply;
uchar
casedn_multiply;
uint
mbminlen;
uint
mbmaxlen;
uint16
min_sort_char;
uint16
max_sort_char;
uchar
pad_char;
my_bool
escape_with_backslash_is_dangerous;
uchar
levels_for_compare;
uchar
levels_for_order;
MY_CHARSET_HANDLER *cset;
MY_COLLATION_HANDLER *coll;
} CHARSET_INFO;
MY_UNICASE_INFO **caseinfo;
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typedef struct my_collation_handler_st
{
my_bool (*init)(struct charset_info_st *, void *(*alloc)(size_t));
Adding a built-in collation
int
(*strnncoll)(struct charset_info_st *,
const uchar *, size_t, const uchar *, size_t, my_bool);
int
(*strnncollsp)(struct charset_info_st *,
const uchar *, size_t, const uchar *, size_t,
my_bool diff_if_only_endspace_difference);
size_t
(*strnxfrm)(struct charset_info_st *,
uchar *dst, size_t dstlen, uint nweights,
const uchar *src, size_t srclen, uint flags);
size_t
(*strnxfrmlen)(struct charset_info_st *, size_t);
my_bool (*like_range)(struct charset_info_st *,
const char *s, size_t s_length,
pchar w_prefix, pchar w_one, pchar w_many,
size_t res_length,
char *min_str, char *max_str,
size_t *min_len, size_t *max_len);
int
(*wildcmp)(struct charset_info_st *,
const char *str,const char *str_end,
const char *wildstr,const char *wildend,
int escape,int w_one, int w_many);
int
(*strcasecmp)(struct charset_info_st *, const char *, const char *);
uint (*instr)(struct charset_info_st *,
const char *b, size_t b_length,
const char *s, size_t s_length,
my_match_t *match, uint nmatch);
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38
Thanks!
How to add a build-in collation in depth – in another
session.
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