ORACLE exercises, oracle

ORACLE exercises, oracle
1. Create a new table a with the same table structure and data as emp.


Create table a as select * from emp;

2. Add primary key constraints




Alter table a add constraint pk_a_01 primary key (EMPNO );


3. Add a field 'birthdate' for 'A', type 'date.


Alter table a add (birthdate date );


4. Change the ename field of Table a to fixed-length Text 16. Before modification, transfer the column data, leave the column empty, and then fill the data back.
Answer:


First, change the column name, create a new column named the previous name, copy the data of this field to the new column, and delete the original column.
Alter table a rename column ename to new_ename;
Alter table a add (ename varchar (16 ));
Update a set ename = substr (trim (new_ename), 1, 16 );
Alter table a drop (new_ename );