pg_collkey 0.5.0

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pg_collkey 0.5.0
Date
Status
Stable
Latest Stable
pg_collkey 0.5.1 —
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Abstract
ICU collation function wrapper
Released By
ccutrer
License
The MIT (X11) License
Resources
Special Files

Extensions

pg_collkey 0.5.0

README

Contents

README for pg_collkey version 0.3

Please read the LICENSE file, which is shipping with this software.


*** DESCRIPTION ***

This is a wrapper to use the collation functions of the ICU library with a
PostgreSQL database server. Using this wrapper, you can specify the desired
locale for sorting UTF-8 strings directly in the SQL query, rather than
setting it during database installation. Default Unicode collation (DUCET)
is supported. You can select whether punctuation should be a primary
collation attribute or not. The level of comparison can be limited (in order
to ignore accents for example). Numeric sequences of strings can be
recognized, so that 'test2' is placed before 'test10'.


*** REQUIREMENTS ***

- PostgreSQL version 8.1.4, http://www.postgresql.org/
  (might run with older versions too, but this is not tested)
- ICU library version 3.4, http://icu.sourceforge.net/
  (might run with older versions too, but this is not tested)


*** INSTALLATION ***

1. Ensure icu-config and pg_config binaries are available to resolve
   compilation flags for ICU and PostgreSQL.
2. Call 'make'.
3. Call 'make install' to install into your PostgreSQL library directory.
   You will probably need to prefix this with "sudo" if you are a non-root
   user.

Now you can use the 'collkey_icu.sql' file to enable the 'collkey' function
for a database.


*** CAVEATS ***

The function will only work if the database encoding is set to UTF-8. This
is a limitation which can be solved in future releases.
Using different locales within one query can slow down perfomance.


*** USAGE ***

collkey (text, text, bool, int4, bool) RETURNS bytea

The first parameter is the UTF-8 string for which you want a collation key.

The second parameter is defining the locale (i.e. 'root' or 'de_DE',
see http://icu.sourceforge.net/ for more information).
Use 'root', if you want a default unicode collation (DUCET).

If the third parameter is true, certain characters (puncuation, etc.) are
processed at the 4th level (after processing of the case), instead of being
processed at the 1st level.

The fourth parameter is selecting the level of collation:
0: default level (usually 3rd level)
1: 1st level, only base characters are compared, accents, upper/lowercases
   (and punctuation, if the third parameter is true) are ignored
2: 2nd level, accents and modifications of characters are taken into account
3: 3rd level, upper/lowercase is evaluated
4: 4th level, other differences are evaluated
5: 5th level, strings are only equal if they contain the same codepoints
   (after normalization)

The fifth parameter enables numeric sorting, if it is set to true.
This means collkey('test 2') < collkey('test 10').

There are shortcuts with fewer parameters, see 'collkey_icu.sql'.

Example:

SELECT name FROM tbl ORDER BY collkey(name, 'fr_FR');  -- french ordering


*** TODO ***

- enable support for non UTF-8 databases