Changing dateType of a column

i need to change the datType of a column:

below the code i thought will work but it is not.

alter table emp rename column insert_time to time_value1 date default (sysdate)

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i know the above query is wrong,can any one provide a good solution

check this will work or not....

alter table tablename modify(coumn_name);

thanks for ur help:

alter table table_name modify column_name datatype

you can do it like this..

SQL> create table insert_time(time varchar(20));

Table created.

SQL> alter table insert_time modify(time date);

Table altered.

SQL>