Constraint Enable

Question

Hi All,
I have created a table like this
CREATE TABLE table2(a NUMBER CONSTRAINT a_pk PRIMARY KEY);
INSERT INTO table2 VALUES(1);
INSERT INTO table2 VALUES(2);
After that i disabled the primary key like this
ALTER TABLE table2 DISABLE CONSTRAINT a_PK;
Then i inserted duplicate values
INSERT INTO table2 VALUES(1);
INSERT INTO table2 VALUES(1);
Now i want to restrict duplicate values in to that column.
for that i have used
ALTER TABLE pt MODIFY CONSTRAINT pt_apk ENABLE NOVALIDATE
cannot validate (RAMESH.a_pk) - primary key violated.
How can we enable the key.
Please help me.
Thanks in advance

Answer 1

user9077483 wrote:
How can we enable the key.The reason it fails - PK is enforced by unique key. So even though you say novalidate existing data and validate new data only, unique key is not capable of that - it fails any duplicate new or old. In order to take advantage of NOVALIDATE you must implement PK via non-unique index:
SQL> CREATE TABLE table2(a NUMBER)
  2  /
Table created.
SQL> CREATE INDEX a_PK on table2(a)
  2  /
Index created.
SQL> ALTER TABLE table2
  2    ADD CONSTRAINT a_PK
  3      PRIMARY KEY(a)
  4      USING INDEX a_PK
  5  /
Table altered.
SQL> INSERT INTO table2 VALUES(1);
1 row created.
SQL> INSERT INTO table2 VALUES(2);
1 row created.
SQL> ALTER TABLE table2 DISABLE CONSTRAINT a_PK;
Table altered.
SQL> INSERT INTO table2 VALUES(1);
1 row created.
SQL> INSERT INTO table2 VALUES(1);
1 row created.
SQL> ALTER TABLE table2 MODIFY CONSTRAINT a_PK ENABLE NOVALIDATE
  2  /
Table altered.
SQL> select * from table2
  2  /
         A
         1
         2
         1
         1
SQL> INSERT INTO table2 VALUES(1);
INSERT INTO table2 VALUES(1)
ERROR at line 1:
ORA-00001: unique constraint (SCOTT.A_PK) violated
SQL> As you can see, non-unique index allows us to ignore existing duplicates but rejects new ones.
SY.