How Can I Achieve Accent-Insensitive Searches in PostgreSQL?
Jan 20, 2025 pm 12:21 PMPostgreSQL's Approach to Accent-Insensitive Searching
Unlike some databases (like Microsoft SQL Server), PostgreSQL doesn't natively support accent-insensitive collations. While PostgreSQL 12 introduced non-deterministic ICU collations offering case and accent insensitivity, these come with performance trade-offs and operational restrictions.
Strategies for Accent-Insensitive Queries in PostgreSQL
Several methods exist to achieve accent-insensitive searching in PostgreSQL:
1. The unaccent
Module:
This module provides the unaccent()
function, removing accents from strings. This allows queries like:
SELECT * FROM users WHERE unaccent(name) = unaccent('João');
However, unaccent()
isn't IMMUTABLE, preventing its use in expression indexes, and it doesn't expand ligatures (e.g., 'Œ').
2. Optimized C Function Wrapper:
To address unaccent()
's limitations, a more efficient solution involves creating an IMMUTABLE C function wrapper:
CREATE OR REPLACE FUNCTION public.f_unaccent(text) RETURNS text LANGUAGE sql IMMUTABLE PARALLEL SAFE STRICT RETURN public.immutable_unaccent(regdictionary 'public.unaccent', );
This allows for the creation of expression indexes:
CREATE INDEX users_unaccent_name_idx ON users(public.f_unaccent(name));
Queries then use the wrapped function:
SELECT * FROM users WHERE f_unaccent(name) = f_unaccent('João');
3. Leveraging pg_trgm
for Pattern Matching and Ligatures:
For more flexible pattern matching and ligature handling, the pg_trgm
module with trigram indexes offers a powerful solution. A trigram GIN index enables case-insensitive searches and similarity detection:
CREATE INDEX users_unaccent_name_trgm_idx ON users USING gin (f_unaccent(name) gin_trgm_ops); SELECT * FROM users WHERE f_unaccent(name) LIKE ('%' || f_unaccent('João') || '%');
Note that pg_trgm
indexes are more resource-intensive than standard B-tree indexes.
Choosing the optimal approach depends on the specific needs of your application, balancing query performance with index maintenance costs and the requirement for ligature handling.
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