Re: Creating a heirarchy of tables in a schema based on FK
- From: TESTAJ3@xxxxxxxxxxxxxx
- To: cicciuxdba@xxxxxxxxx
- Date: Wed, 18 Nov 2009 08:38:34 -0500
Alan, Oracle does do on delete cascade, you put it in when adding the FK,
did you mean on update cascade? Or am I missing something here,
This is right out of the 9i docs.
CREATE TABLE dept_20
(employee_id NUMBER(4) PRIMARY KEY,
last_name VARCHAR2(10),
job_id VARCHAR2(9),
manager_id NUMBER(4) CONSTRAINT fk_mgr
REFERENCES employees ON DELETE SET NULL,
hire_date DATE,
salary NUMBER(7,2),
commission_pct NUMBER(7,2),
department_id NUMBER(2) CONSTRAINT fk_deptno
REFERENCES departments(department_id)
ON DELETE CASCADE );
joe
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From:
Guillermo Alan Bort <cicciuxdba@xxxxxxxxx>
To:
stbaldwin@xxxxxxxxxxxxxxxx
Cc:
Steven.Rebello@xxxxxxxxxx, "oracle-l@xxxxxxxxxxxxx"
<oracle-l@xxxxxxxxxxxxx>
Date:
11/18/2009 08:05 AM
Subject:
Re: Creating a heirarchy of tables in a schema based on FK
Sent by:
oracle-l-bounce@xxxxxxxxxxxxx
Hierarchycal (?) models are difficult to use, specially since RDBMS allow
for multiple table relations (that's what the relational is all about ;-)
)
AFAIK, Oracle does not support the ON DELETE CASCADE per se, at least it
doesn't in 10g (and earlier). You can emulate that using PL/SQL and/or
triggers.
You can use a brute force approach, running many the delete on all the
tables sorted in an arbitrary order... eventually (after four or five
runs) you'll have all the tables clear. NOT the best approach, just the
fastest to write :-P
Alternativeley, you can use recursion, but might not work in all
relational situations.
hth
Alan Bort
Oracle Certified Professional
On Wed, Nov 18, 2009 at 5:12 AM, Steve Baldwin <stbaldwin@xxxxxxxxxxxxxxxx
> wrote:
Could you just change the FK constraints to 'ON DELETE CASCADE' then
just delete from the top level table(s)? This is by far the least
amount of work.
Alternatively, you could write a recursive function that fetches from
user_constraints and user_cons_columns and uses either dbms_sql or
execute immediate (depending on your Oracle version) to execute the
delete statement.
Hope this helps.
On Wed, Nov 18, 2009 at 6:30 PM, Steven Rebello
<Steven.Rebello@xxxxxxxxxx> wrote:
> Hi List members
>
> Would like your help/inputs in a problem I am facing here.
>
> I want to clear out records from a huge bunch of selected tables (1000+)
which have interdependencies established using FK constraints. Of course,
just creating a "delete * from table" doesn't work because of the FK
constraints.
>
> What I want to do is to identify the "child" tables which can be deleted
first and then create the hierarchy of tables so that the parent tables
can then be cleared out, and so on.
>
> Can anyone point me to any reference or script which can generate this
hierarchy based on the foreign key constraints? Based on that I can then
make the delete script pretty quickly.
>
> I thought of disabling the constraints and re-enabling them after the
"delete * from table" script, but would like to try the cleaner approach
of starting from the bottom of the dependency tree for these tables.
>
> Thanks
> Steven Rebello
> MASTEK LTD.
> Mastek is in NASSCOM's 'India Top 20' Software Service Exporters List.
> In the US, we're called MAJESCOMASTEK
>
>
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