While you are trying to truncate table you can hit ORA-02266: error.

In this post I am going to make demo and share solution steps.

I assume that We have 2 tables. Test and Test2. Those table have relation between each other.

Let us try to truncate test table first

SQL>truncate table test;
truncate table test
*
ERROR at line 1:
ORA-02266: unique/primary keys in table referenced by enabled foreign keys

It gives some records have relation with some other records.

There are 2 options now.

1. Easy way is using The TRUNCATE TABLE … CASCADE command succeeds and recursively truncates all the dependent tables.
2.Other way which is related with this post. Now let us follow option 2

Let us disable constraints first;

SQL>select 'alter table '||a.owner||'.'||a.table_name||' disable constraint '||a.constraint_name||';'
from all_constraints a, all_constraints b
where a.constraint_type = 'R'
and a.r_constraint_name = b.constraint_name
and a.r_owner = b.owner
and a.owner= 'USER1,USER2'; -- ---> If you want to drop many tables under different schemas

'ALTERTABLE'||A.OWNER||'.'||A.TABLE_NAME||'DISABLECONSTRAINT'||A.CONSTRAINT_NAME||';'
---------------------------------------------------------------------------------------------------------------------------------------------------
alter table GUNES.TEST disable constraint FK_NO;
alter table GUNES.TEST2 disable constraint FK_NO2;

SQL> alter table GUNES.TEST disable constraint FK_NO;

Table altered.

SQL>truncate table test;

Table truncated.

Now Let us enable constraints again;

SQL>select 'alter table '||a.owner||'.'||a.table_name||' enable constraint '||a.constraint_name||';'
from all_constraints a, all_constraints b
where a.constraint_type = 'R'
and a.r_constraint_name = b.constraint_name
and a.r_owner = b.owner
and a.owner= 'USER1,USER2'; -- ---> If you want to drop many tables under different schemas

'ALTERTABLE'||A.OWNER||'.'||A.TABLE_NAME||'ENABLECONSTRAINT'||A.CONSTRAINT_NAME||';'
----------------------------------------------------------------------------------------------------------------------------------
alter table GUNES.TEST enable constraint FK_NO;

SQL>alter table GUNES.TEST enable constraint FK_NO; *
ERROR at line 1:
ORA-02298: cannot validate (GUNES.FK_NO) - parent keys not found

As you can see now We got ORA-02298.So We are hitting this error because an alter table validating constraint failed because the table has orphaned child records.

So What is solutions:

Solution 1: delete child record
Solution 2: enable constraint with novalidate

SQL>select 'alter table '||a.owner||'.'||a.table_name||' enable novalidate constraint '||a.constraint_name||';'
from all_constraints a, all_constraints b
where a.constraint_type = 'R'
and a.r_constraint_name = b.constraint_name
and a.r_owner = b.owner
and a.owner= 'USER1,USER2'; -- ---> If you want to drop many tables under different schemas

'ALTERTABLE'||A.OWNER||'.'||A.TABLE_NAME||'ENABLENOVALIDATECONSTRAINT'||A.CONSTR
--------------------------------------------------------------------------------
alter table GUNES.TEST enable novalidate constraint FK_NO;

SQL> alter table GUNES.TEST enable novalidate constraint FK_NO;

Table altered.