upper(t) and lower(t) returns the ASCII characters of t in upper or lowercase. The non ASCII characters (such as the ä, é) are returned unchanged. This is demonstrated in the following simple example:
create table tq84_tab (
id int primary key,
val text
);
insert into tq84_tab values (1, 'foo');
insert into tq84_tab values (2, 'Bar');
insert into tq84_tab values (3, 'BAZ');
insert into tq84_tab values (4, 'äÖé');
insert into tq84_tab values (5, 'üzz');
.mode column
.width 3 3 3 3
select
id,
val,
lower(val) val_l,
upper(val) val_u
from
tq84_tab;
--
-- 1 foo foo FOO
-- 2 Bar bar BAR
-- 3 BAZ baz BAZ
-- 4 äÖé äÖé äÖé
-- 5 üzz üzz üZZ
select * from tq84_tab where val = upper(val);
--
-- 3 BAZ
-- 4 äÖé
select * from tq84_tab where val = lower(val);
--
-- 1 foo
-- 4 äÖé
-- 5 üzz