feat: add Unicode-aware expression indexes for German umlaut search#261
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SQLite's LOWER() only handles ASCII — LOWER('Ä') returns 'Ä', not 'ä'.
Add expression indexes using REPLACE(REPLACE(REPLACE(LOWER(...), 'Ä', 'ä'),
'Ö', 'ö'), 'Ü', 'ü')) for all columns used in ahb-tabellen search.
These indexes enable the LIKE optimization for prefix queries (startsWith)
when the search code uses the matching REPLACE expression. Substring queries
(%pattern%) always do full scans regardless of indexes.
Related: Hochfrequenz/ahb-tabellen#790
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Summary
Add expression indexes using
REPLACE(REPLACE(REPLACE(LOWER(...), 'Ä', 'ä'), 'Ö', 'ö'), 'Ü', 'ü'))for all columns used in ahb-tabellen's global search.Why
SQLite's
LOWER()only handles ASCII. The existinglower()expression indexes storeÄas uppercase, which doesn't match when the search pattern uses lowercaseä(from JavaScript's correct.toLowerCase()). See Hochfrequenz/ahb-tabellen#790.These indexes enable SQLite's LIKE optimization for prefix queries (
startsWith) when ahb-tabellen uses the matching REPLACE expression in its queries.Columns indexed
beschreibung,segmentgroup_id,segment_id,dataelement_id,code_description,code_value,line_ahb_status,line_name— matching the 8 existinglower()indexes.Companion PR
Hochfrequenz/ahb-tabellen#798 updates the search queries to use the matching REPLACE expression.