yes, the database stores the data how you submit it.
if you say:
INSERT INTO MyTable (LowerCase, UpperCase) VALUES ("abcd", "ABCD");
it will insert:
LowerCase | UpperCase
abcd | ABCD
if you do
INSERT INTO MyTable (LowerCase, UpperCase) VALUES ("AbCd", "aBcD");
it will insert:
LowerCase | UpperCase
AbCd | aBcD
it's up to you to sanitize the inputs to the case you want, or just let it go as entered.
however, when I do a
SELECT * FROM MyTable WHERE LowerCase="abcd";
it will return both entries.