How to delete the primary key from without using constraint name - oracle

Question

CREATE TABLE Persons (
ID int PRIMARY KEY,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Age int
);
How to remove the primary key as there is no constraint defined?

Answer 1

"How to remove PK as there is no constraint defined?"
Actually it's every bit as simple as you might hope:
SQL> create table t23 (id number primary key);
Table created.
SQL> select constraint_name, constraint_type
2 from user_constraints
3 where table_name = 'T23'
4 /
CONSTRAINT_NAME C
------------------------------ -
SYS_C0034419 P
SQL> alter table t23 drop primary key;
Table altered.
SQL> select constraint_name, constraint_type
2 from user_constraints
3 where table_name = 'T23'
4 /
no rows selected
SQL>

Answer 2

run this to get constraint name :
SELECT *
FROM user_cons_columns
WHERE table_name = Persons;
then run
ALTER TABLE Persons
DROP CONSTRAINT <pk constraint>;

Answer 3

Don't think you can do it in 1 SQL command,without knowing the constraint name, but you can know the constraint name as in this case it would be defined by system. Something which starts with SYS.....
Alternatively you can use a PLSQL block to achieve the same.
See the example below for your case.
CREATE TABLE Persons (
ID int PRIMARY KEY,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Age int
);
Find constraint name
select CONSTRAINT_NAME
From USER_CONSTRAINTS
where table_name='PERSONS'
AND CONSTRAINT_TYPE='P';
OUTPUT:= SYS_C0012152
Drop Constraint
ALTER TABLE PERSONS
DROP CONSTRAINT SYS_C0012152;
Note: The constraint name SYS_C0012152 is not enclosed in single quotes.
PLSQL Block to do the same
declare
sql_stmt varchar2(255);
cons_name varchar2(30);
begin
select CONSTRAINT_NAME
into cons_name
From USER_CONSTRAINTS
where table_name='PERSONS'
AND CONSTRAINT_TYPE='P';
sql_stmt:=' ALTER TABLE PERSONS
DROP CONSTRAINT '||cons_name;
dbms_output.put_line(sql_stmt);
execute immediate sql_stmt;
end;