Compare Strings in Oracle

class    teacher
-----------------
Mat101   Smith
MAT101   Jones
mat101   Abram
ENG102   Smith

Select teacher From classes where lower(class) = 'math101'

SQL> WITH LETTERS AS
  2  (SELECT 'a' LETTER FROM DUAL UNION ALL
  3   SELECT 'b' LETTER FROM DUAL UNION ALL
  4   SELECT 'A' LETTER FROM DUAL UNION ALL
  5   SELECT 'B' LETTER FROM DUAL)
  6  SELECT LETTER FROM LETTERS
  7  WHERE LETTER = 'A';

L
-
A

SQL>

SQL> ALTER SESSION SET NLS_SORT=BINARY_CI;

Session altered.

SQL> ALTER SESSION SET NLS_COMP=LINGUISTIC;

Session altered.

SQL> WITH LETTERS AS
  2  (SELECT 'a' LETTER FROM DUAL UNION ALL
  3   SELECT 'b' LETTER FROM DUAL UNION ALL
  4   SELECT 'A' LETTER FROM DUAL UNION ALL
  5   SELECT 'B' LETTER FROM DUAL)
  6  SELECT LETTER FROM LETTERS
  7  WHERE LETTER = 'A';

L
-
a
A

Select teacher From classes where class in (lower('mat101'), upper('mat101'), initcap('mat1010')).

Select teacher From classes where lower(class) = LOWER('math101')