title: How to change timezone of Oracle 9i Database
body: <p>How to change Oracle 9i database timezone, 
  I have a user schema with name 'HR_NU', its timezone is -07:00, I want to change it using alter query</p>
  
  <pre><code>alter database set time_zone='+05:00';
  </code></pre>
  
  <p>but getting errors</p>
  
  <pre><code>Error starting at line 10 in command:
  alter database set time_zone='+05:00'
  Error report:
  SQL Error: ORA-02231: missing or invalid option to ALTER DATABASE
  02231. 00000 -  "missing or invalid option to ALTER DATABASE"
  *Cause:    An option other than ADD, DROP, RENAME, ARCHIVELOG, NOARCHIVELOG,
             MOUNT, DISMOUNT, OPEN, or CLOSE is specified in the statement.
  *Action:   Specify only legal options.
  </code></pre>
  
  <p>I google same issue, and came to know that if I have a  table containing a field of datatype timestamp with localtimezone then I will get above error, the solution suggested is change datatype of each column having datatype timestamp, but I have more than 300 tables, and about 200 columns of timestamp datatype.</p>
  
  <p>Any help please.</p>