How to remove/Delete the effect of UNIQUE KEY from TABLE - sql

Question

I have UNIQUE KEY attribute on my Table. For my project I deleted that UNIQUE KEY from table , but when try to enter data it still giving the error of UNIQUE KEY VIOLATION.
Already done
to check to commit the database .
to refreshed the entire database.
to find that CONSTRAINT on schema.
SELECT DISTINCT table_name
FROM all_indexes
WHERE index_name = 'CONSTRAINT_NAME';
The above query returns no data (Constraint not found).
I want my data duplicate for one employee without UNIQUE KEY VIOLATION ERROR

Answer 1

Below are some of the queries you can run and check if there is specified index, constraints exist on the table and once you find you can simply drop it. Maybe your unique index was created before the constraint was created:
SELECT * FROM user_cons_columns WHERE table_name = '<your table name>';
select column_name from user_ind_columns where index_name = '<index_name>';
select column_name from user_cons_columns where constraint_name = '<index_name>';
Use below command for dropping index:
DROP INDEX index_name;
Use below command for dropping constraints:
ALTER TABLE <table_name>
DROP CONSTRAINT <constraint_name>

Answer 2

[TL;DR] If you have a UNIQUE INDEX without a UNIQUE CONSTRAINT then you will get the same error message. You need to make sure you have dropped both the index and the constraint.
CREATE TABLE test_data ( id NUMBER );
CREATE UNIQUE INDEX test_data__id__u ON test_data ( id );
ALTER TABLE test_data ADD CONSTRAINT test_data__id__u UNIQUE ( id );
INSERT INTO test_data ( id ) VALUES ( 1 );
INSERT INTO test_data ( id ) VALUES ( 1 );
Will insert one row and will give ORA-00001: unique constraint (FIDDLE_ALGCPMTPWFJZCXIPXNLR.TEST_DATA__ID__U) violated for the second.
If you do:
SELECT * FROM user_constraints WHERE table_name = 'TEST_DATA';
SELECT * FROM user_indexes WHERE table_name = 'TEST_DATA';
Then it will show there is an index and a constraint on the table.
Then if you drop the constraint:
ALTER TABLE test_data DROP CONSTRAINT test_data__id__u;
and try to do:
INSERT INTO test_data ( id ) VALUES ( 1 );
Then you will get:
ORA-00001: unique constraint (FIDDLE_ALGCPMTPWFJZCXIPXNLR.TEST_DATA__ID__U) violated
If you look at the indexes and constraints again:
SELECT * FROM user_constraints WHERE table_name = 'TEST_DATA';
SELECT * FROM user_indexes WHERE table_name = 'TEST_DATA';
Then it will show no constraints but the index is still there. You need to make sure the unique index has been dropped too.
DROP INDEX test_data__id__u;
INSERT INTO test_data ( id ) VALUES ( 1 );
Will then insert the row.
db<>fiddle here