generated by default as identity for varchar data type in sql - sql

Question

I have a table xx_abc with data existing in the database.
I want to add a column confi_name in this table which is mandatory column.
If i add this column like
ALTER TABLE xx_abc
ADD
( confi_NAME VARCHAR2(2000) NOT NULL);
I am getting an error :
Error report:
SQL Error: ORA-01758: table must be empty to add mandatory (NOT NULL) column
01758. 00000 - "table must be empty to add mandatory (NOT NULL) column"
So I converted it to
ALTER TABLE xx_abc
ADD
( confi_name VARCHAR2(2000) generated by default as identity (START WITH 2, INCREMENT BY 1)
But this is also throwing an error because generated by defaut has to be of int data type. I basically want to make config_name with value which is unique for each row. and i cannot change its data type as well. Any work around ?

Answer 1

First add the column as nullable.
Then update that column with a default value in every row.
Then set the column to be NOT NULL.

Answer 2

As you have mentioned, the table had their values already. If you are going to add another column with "not null" property, make sure that you insert values equal to the number of values(rows) of the previous columns since you had set it to "not null" as its properties. Another way is not to use "not null" first then set the property to "not null" once you have enough values for the column already.

Answer 3

you have to set a default value for the existing rows before adding the constraint.
1)Modify the table
ALTER TABLE xx_abc
ADD
( confi_NAME VARCHAR2(2000));
2)Set default values
update XX_ABC set confi_NAME = 'DEFAULT';
COMMIT;
3)Add the constraint
alter table XX_ABC add check (confi_NAME is not null);

Answer 4

Existing table:
SQL> CREATE TABLE t(A VARCHAR2(10));
Table created.
SQL> INSERT INTO t VALUES('a');
1 row created.
SQL> INSERT INTO t VALUES('b');
1 row created.
SQL> INSERT INTO t VALUES('c');
1 row created.
SQL> COMMIT;
Commit complete.
Add a new column:
SQL> ALTER TABLE t ADD (b VARCHAR2(10));
Table altered.
Update the rows:
SQL> UPDATE t SET b = 'newvalue';
3 rows updated.
Add NOT NULL constraint:
SQL> ALTER TABLE t MODIFY b NOT NULL;
Table altered.
SQL> desc t
Name Null? Type
----------------------------------------- -------- -------------
A VARCHAR2(10)
B NOT NULL VARCHAR2(10)
SQL>