Postgres 11 | db<>fiddle

SELECT upper('é' collate "C") AS "C", upper('é' collate "C.UTF-8") AS "C.UTF-8", upper('é' collate "ucs_basic") AS "ucs_basic";

C	C.UTF-8	ucs_basic
é	É	é
…

hidden batch(es)

SELECT 'A' AS "0041", E'\u0378' AS "0378", ('A' < E'\u0378' collate "C") AS "C", ('A' < E'\u0378' collate "C.UTF-8") AS "C.UTF-8", ('A' < E'\u0378' collate "ucs_basic") AS "ucs_basic", ('A' < E'\u0378' collate "en_GB") AS "en_GB";

0041	0378	C	C.UTF-8	ucs_basic	en_GB
A	͸	t	f	t	f
…

hidden batch(es)

SELECT E'\u0379' AS "0379", E'\u0378' AS "0378", (E'\u0379' < E'\u0378' collate "C") AS "C", (E'\u0379' < E'\u0378' collate "C.UTF-8") AS "C.UTF-8", (E'\u0379' < E'\u0378' collate "ucs_basic") AS "ucs_basic", (E'\u0379' < E'\u0378' collate "en_GB") AS "en_GB";

0379	0378	C	C.UTF-8	ucs_basic	en_GB
͹	͸	f	f	f	f
…

hidden batch(es)

SELECT E'\u0020' AS "0020", E'\u0378' AS "0378", (E'\u0020' < E'\u0378' collate "C") AS "C", (E'\u0020' < E'\u0378' collate "C.UTF-8") AS "C.UTF-8", (E'\u0020' < E'\u0378' collate "ucs_basic") AS "ucs_basic", (E'\u0020' < E'\u0378' collate "en_GB") AS "en_GB";

0020	0378	C	C.UTF-8	ucs_basic	en_GB
	͸	t	f	t	t
…

hidden batch(es)

SELECT E'\u0001' AS "0001", E'\u0378' AS "0378", (E'\u0001' < E'\u0378' collate "C") AS "C", (E'\u0001' < E'\u0378' collate "C.UTF-8") AS "C.UTF-8", (E'\u0001' < E'\u0378' collate "ucs_basic") AS "ucs_basic", (E'\u0001' < E'\u0378' collate "en_GB") AS "en_GB";

0001	0378	C	C.UTF-8	ucs_basic	en_GB
	͸	t	t	t	t
…

hidden batch(es)

SELECT 'A' AS "0041", E'\u0377' AS "0377", ('A' < E'\u0377' collate "C") AS "C", ('A' < E'\u0377' collate "C.UTF-8") AS "C.UTF-8", ('A' < E'\u0377' collate "ucs_basic") AS "ucs_basic", ('A' < E'\u0377' collate "en_GB") AS "en_GB";

0041	0377	C	C.UTF-8	ucs_basic	en_GB
A	ͷ	t	t	t	f
…

hidden batch(es)

SELECT E'\u00E9' AS "00E9", E'\u00D3' AS "00D3", (E'\u00E9' < E'\u00D3' collate "C") AS "C", (E'\u00E9' < E'\u00D3' collate "C.UTF-8") AS "C.UTF-8", (E'\u00E9' < E'\u00D3' collate "ucs_basic") AS "ucs_basic", (E'\u00E9' < E'\u00D3' collate "en_GB") AS "en_GB";

00E9	00D3	C	C.UTF-8	ucs_basic	en_GB
é	Ó	f	f	f	t
…

hidden batch(es)

SELECT E'\u0510' AS "0510", E'\u08BA' AS "08BA", (E'\u0510' < E'\u08BA' collate "C") AS "C", (E'\u0510' < E'\u08BA' collate "C.UTF-8") AS "C.UTF-8", (E'\u0510' < E'\u08BA' collate "ucs_basic") AS "ucs_basic", (E'\u0510' < E'\u08BA' collate "en_GB") AS "en_GB";

0510	08BA	C	C.UTF-8	ucs_basic	en_GB
Ԑ	ࢺ	t	t	t	t
…

hidden batch(es)

SELECT ('ab' < 'a-c' collate "C") AS "C", ('ab' < 'a-c' collate "C.UTF-8") AS "C.UTF-8", ('ab' < 'a-c' collate "ucs_basic") AS "ucs_basic", ('ab' < 'a-c' collate "en_GB") AS "en_GB";

C	C.UTF-8	ucs_basic	en_GB
f	f	f	t
…

hidden batch(es)

select * from pg_collation where collprovider='c' order by "collname";

collname	collnamespace	collowner	collprovider	collencoding	collcollate	collctype
C	11	10	c	-1	C	C
C.UTF-8	11	10	c	6	C.UTF-8	C.UTF-8
POSIX	11	10	c	-1	POSIX	POSIX
en_GB	11	10	c	6	en_GB.utf8	en_GB.utf8
en_GB.utf8	11	10	c	6	en_GB.utf8	en_GB.utf8
ucs_basic	11	10	c	6	C	C
…

hidden batch(es)