README.PostgreSQL
Locale and sorting behavior (order by)
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The sorting behavior in the PostgreSQL database, and therefore in RT,
can change depending on the locale settings. RT is commonly run with
locales like en_US.UTF-8, en_GB.UTF-8, etc., which will process sort
order in a case-insensitive way. Other locales, like C.UTF-8, are
case sensitive. If you see unexpected sort order in RT, either after
an initial installation or after an upgrade, confirm that the locale
is set correctly.
More information: https://www.postgresql.org/docs/12/locale.html