Collation

Case support in PostgreSQL (lower() and upper() functions) depend on the current collation rules. A table has a default collation which is specified at creation (with a default). To remove the dependency on the table’s collation, you can specify the desired collation explicitly.

Note that PostgreSQL can be compiled with or without support for libicu, as a complement to the collation support in your libc.

Using different collation rules

ELISP> (let ((res (pg-exec *pg* "SELECT lower('FÔÖÉ' COLLATE \"fr_FR\")")))
         (car (pg-result res :tuple 0)))
"fôöé"
ELISP> (let ((res (pg-exec *pg* "SELECT lower('FÔ🐘💥bz' COLLATE \"fr_FR\")")))
         (car (pg-result res :tuple 0)))
"fô🐘💥bz"
ELISP> (pg-result (pg-exec *pg* "CREATE COLLATION IF NOT EXISTS \"french\" (provider = icu, locale = 'fr_FR')") :status)
"CREATE COLLATION"
ELISP> (let ((res (pg-exec *pg* "SELECT lower('FÔÖÉ' COLLATE \"french\")")))
         (car (pg-result res :tuple 0)))
"fôöé"

Using pg-el

Collation