Oracle Error Message
ORA-01743: only pure functions can be indexed
Reason for the Error
The indexed function uses SYSDATE or the user environment.
Solution
PL/SQL functions must be pure (RNDS, RNPS, WNDS, WNPS). SQL expressions must not use SYSDATE, USER, USERENV(), or anything else dependent on the session state. NLS-dependent functions are OK.