Localized COLLATE on a SQLite string comparison - unicode

Question

I want to compare two strings in a SQLite DB without caring for the accents and the case. I mean "Événement" should be equal to "evenèment".
On Debian Wheezy, the SQLite package doesn't provide ICU. So I compiled the official SQLite package (version 3.7.15.2 2013-01-09 11:53:05) with contains an ICU module. Now, I do have a better Unicode support (the originallower() applied only to ASCII chars, now it works on other letters). But I can't manage to apply a collation to a comparison.
SELECT icu_load_collation('fr_FR', 'FRENCH');
SELECT 'événement' COLLATE FRENCH = 'evenement';
-- 0 (should be 1)
SELECT 'Événement' COLLATE FRENCH = 'événement';
-- 0 (should be 1 if collation was case-insensitive)
SELECT lower('Événement') = 'événement';
-- 1 (at least lower() works as expected with Unicode strings)
The SQLite documentation confirms that this is the right way to apply a collation. I think the documentation of this ICU extension is a bit light (few examples, nothing on case sensitivity for collations).
I don't understand why the COLLATE operator has no effect in my example above. Please help.

Answer 1

I took me hours to understand the situation... The way the ICU collations are defined in SQLite has (almost) no incidence on comparisons. An exception being, according to the ICU, Hebrew texts with cantillation marks. This is the default behavior of the ICU library's collation. With SQLite, LIKE becomes case-insensitive when ICU is loaded, but normalization of the accentuated letters can't be attained this way.
I finally understood that what I needed was to set the
strength
of the collation to the
primary level
instead of the default tertiary level.
I found no way to set this through the locale
(e.g several variants of SELECT icu_load_collation('fr_FR,strength=0', 'french') were useless).
So the only solution was to patch the code of SQLite.
It was easy thanks to the ucol_setStrength() function
in the ICU API.
The minimal change is a one-line patch: add the line ucol_setStrength(pUCollator, 0); after pUCollator = ucol_open(zLocale, &status); in the function icuLoadCollation().
For a backwards-compatible change, I added an optional third parameter to icu_load_collation() that sets the strength:
0 for default, 1 for primary, etc. up to 4-quaternary.
See the diff.
At last I have what I wanted:
SELECT icu_load_collation('fr_FR', 'french_ci', 1); -- collation with strength=primary
SELECT 'Événement' COLLATE french_ci = 'evenèment';
-- 1