Does PostgreSQL support “accent insensitive” collations?

Question

In Microsoft SQL Server, it\'s possible to specify an \"accent insensitive\" collation (for a database, table or column), which means that it\'s possible for a query like

Answer 1

No, PostgreSQL does not support collations in that sense

PostgreSQL does not support collations like that (accent insensitive or not) because no comparison can return equal unless things are binary-equal. This is because internally it would introduce a lot of complexities for things like a hash index. For this reason collations in their strictest sense only affect ordering and not equality.

Workarounds

Full-Text-Search Dictionary that Unaccents lexemes.

For FTS, you can define your own dictionary using unaccent,

CREATE EXTENSION unaccent;

CREATE TEXT SEARCH CONFIGURATION mydict ( COPY = simple );
ALTER TEXT SEARCH CONFIGURATION mydict
  ALTER MAPPING FOR hword, hword_part, word
  WITH unaccent, simple;

Which you can then index with a functional index,

-- Just some sample data...
CREATE TABLE myTable ( myCol )
  AS VALUES ('fóó bar baz'),('qux quz');

-- No index required, but feel free to create one
CREATE INDEX ON myTable
  USING GIST (to_tsvector('mydict', myCol));

You can now query it very simply

SELECT *
FROM myTable
WHERE to_tsvector('mydict', myCol) @@ 'foo & bar'

    mycol    
-------------
 fóó bar baz
(1 row)

See also

• Creating a case-insensitive and accent/diacritics insensitive search on a field

Unaccent by itself.

The unaccent module can also be used by itself without FTS-integration, for that check out Erwin's answer