Modify the Data Type of a table field in ORACLE

To modify the Data Type of a table field in ORACLE, you need to use a backup field to change the table as follows:

Alter table tablename alter column colname newDataType

 

For example:

Alter table mytable alter column mycol1 int default 0

 

Later, I implemented it. I checked the information and said this (or not ):

Alter table userreg modify column bak2 VARCHAR2 (20) default to_char (sysdate, 'yyyy-MM-DD HH24: MI: ss ')

 

After practice, Oracle had to change it like this (and ensure that the column has no data; otherwise, it cannot be changed ):

Alter table userreg modify (bak2 varchar2 (26) default to_char (sysdate, 'yyyymmddhh24miss '))

 

Or:

Alter table userreg modify (bak2 char (21) default to_char (current_date, 'yyyy-MM-DD HH24: MI: ss '))