Oracle 11g Release 2

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SELECT TO_TIMESTAMP(sysdate) FROM dual

TO_TIMESTAMP(SYSDATE)

20-FEB-20 12.00.00 AM

ALTER SESSION SET NLS_TIMESTAMP_FORMAT = 'YYYY-MM-DD HH24:MI:SS.FF9';
SELECT TO_TIMESTAMP(sysdate) FROM dual

TO_TIMESTAMP(SYSDATE)

0020-02-20 00:00:00.000000000

ALTER SESSION SET NLS_TIMESTAMP_FORMAT = 'FXYYYY-MM-DD HH24:MI:SS.FF9';
SELECT TO_TIMESTAMP(sysdate) FROM dual
ORA-01862: the numeric value does not match the length of the format item