EXTRACT

Convert a numeric or date expression to a character String.

Syntax
      EXTRACT (type FROM datetime | interval)

Key
Types that can be extracted:
  YEAR
  MONTH
  DAY
  HOUR
  MINUTE
  SECOND
  TIMEZONE_HOUR
  TIMEZONE_MINUTE
  TIMEZONE_REGION
  TIMEZONE_ABBR

Examples

SQL> SELECT EXTRACT(YEAR FROM DATE '2009-01-04') FROM dual;

SQL> Select expiry_date,
Extract(YEAR from expiry_date) YR,
Extract(month from expiry_date) MTH
From dba_users
Where expiry_date is not null; 

SQL> select to_char(sysdate,'HH24:MI:SS') "Time Now" from dual;
 '14:35:56'

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Related

Oracle SQL Functions
TO_DATE - Convert to a date
TO_NUMBER - Convert to numeric format
CONVERT - Convert a string from one character set to another.
ORA-00932 inconsistent datatypes