On deferred segment creation and truncate

One year ago, I wrote about a side effect of deferred segment creation and drop tablespace :
on deferred segment creation

Today I discoved one more side effect :

In the good old days (I read once that you are old as soon as you start talking about the good old days) and according to the doc :
You cannot truncate the parent table of an enabled foreign key constraint. You must disable the constraint before truncating the table


SQL> alter session set deferred_segment_creation=false;

Session altered.

SQL> create table t1(x number primary key);

Table created.

SQL> create table t2(x number references t1);

Table created.

SQL> truncate table t1;
truncate table t1
               *
ERROR at line 1:
ORA-02266: unique/primary keys in table referenced by enabled foreign keys

This however does not apply if you have deferred segment creation and empty tables


SQL> alter session set deferred_segment_creation=true;

Session altered.

SQL> create table t1(x number primary key);

Table created.

SQL> create table t2(x number references t1);

Table created.

SQL> truncate table t1;

Table truncated.

Table truncated. Ok, what’s the point in truncating an empty table …

Published by

Laurent Schneider

Oracle Certified Master

3 thoughts on “On deferred segment creation and truncate”

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