FOREIGN KEY Constraint And Table Lock

According to Db Concepts on Data Integrity->Types of Integrity Contraints->Referential Integrity Constraints, if the FK column is not indexed, delete/update of parent table would cause child table share locked.
I can understand the reason behind this behaviour because if parent's PK is modified but not commited yet, we don't want another transaction to insert/update the child's FK column to use the deleted parent PK value and this requires a table share lock.
The problem is, I don't understand why if the child's FK is indexed, no table share lock is acquired. The same condition could happen and we still need to prevent another transaction from using the uncommitted deleted PK in parent as the child's FK.
Appreciate and advice.

hi
When PK column change, Oracle is going to have to do a
referential integrity check on any referenced columns ,in
the absence of an index on the child end of the foreign
key, that would seem to result in a full table scan of the table which cause locks the entire table for any
Delete or Update on Parent table.
Khurram

Similar Messages

FOREIGN KEY CONSTRAINT 의 MASTER TABLE NAME 의 확인

제품 : ORACLE SERVER
작성날짜 : 1995-11-02
FOREIGN KEY CONSTRAINT 의 MASTER TABLE NAME 의 확인
===================================================
다음은 FOREIGN KEY CONSTRAINT 이름으로 REFERENCE 하는 TABLE
(MASTER TABLE)을 찾는 SQL SCRIPT이다.
col Primary_key_table format a20
col Constraint_name format a20
select a.object_name Primary_Key_table,
c.name Constraint_name
from dba_objects a,
sys.cdef$ b,
sys.con$ c
where c.name = 'EMP_FOREIGN_KEY' -- CONSTRAINT NAME
and b.con# = c.con#
and b.robj# = a.object_id
/

The set of constraints as you show it is valid, but will likely result in a lot of violations since both child columns are larger than the parent. The Oracle 2256 error has nothing to do with data validation, nor with the different lengths of the columns. The documentation says
02256, 00000, "number of referencing columns must match referenced columns"
// *Cause: The number of columns in the foreign-key referencing list is not
// equal to the number of columns in the referenced list.
// *Action: Make sure that the referencing columns match the referenced
// columns.Look at the actual statement that the client ran. It will be different than the one you posted. one of the two column lists will have more columns than the other.

FOREIGN KEY CONSTRAINT의 MASTER TABLE을 REFERENCE하는 TABLE 찾기

제품 : SQL*PLUS
작성날짜 : 2003-12-17
FOREIGN KEY CONSTRAINT의 MASTER TABLE을 REFERENCE하는 TABLE 찾기
================================================================
Master table 이 dept2일 때, 이 테이블을 참조하는 table들을 찾는 SQL
select x.table_name "reference table"
from
(select distinct r_constraint_name,table_name
from all_constraints
where constraint_type='R' ) x, all_constraints a
where a.table_name = 'DEPT2'
and x.r_constraint_name = a.constraint_name;

Using FOreign key constraints on tables in database.

I am student and novice in the field of ORACLE and PL/SQL and Database Creation. I had created a database consisting tables and got problem while applying foreign key constraints.
CUST_MSTR
CREATE TABLE "DBA_BANKSYS"."CUST_MSTR"("CUST_NO" VARCHAR2(10),
"FNAME" VARCHAR2(25), "MNAME" VARCHAR2(25), "LNAME" VARCHAR2(25),
"DOB_INC" DATE NOT NULL,      "OCCUP" VARCHAR2(25), "PHOTOGRAPH" VARCHAR2(25),
"SIGNATURE" VARCHAR2(25), "PANCOPY" VARCHAR2(1),      "FORM60" VARCHAR2(1));
(CUST_NO is PRIMARY KEY, )
-- EMP_MSTR
CREATE TABLE "DBA_BANKSYS"."EMP_MSTR"("EMP_NO" VARCHAR2(10),
"BRANCH_NO" VARCHAR2(10), "FNAME" VARCHAR2(25), "MNAME" VARCHAR2(25),
"LNAME" VARCHAR2(25), "DEPT" VARCHAR2(30), "DESIG" VARCHAR2(30));
(EMP_NO is primary key )
--NOMINEE_MSTR
CREATE TABLE "DBA_BANKSYS"."NOMINEE_MSTR"("NOMINEE_NO" VARCHAR2(10),
"ACCT_FD_NO" VARCHAR2(10), "NAME" VARCHAR2(75), "DOB" DATE,
RELATIONSHIP" VARCHAR2(25));
(NOMINEE_NO is primary key )
--ADDR_DTLS
CREATE TABLE "DBA_BANKSYS"."ADDR_DTLS"("ADDR_NO" NUMBER(6),
"CODE_NO" VARCHAR2(10),      "ADDR_TYPE" VARCHAR2(1), "ADDR1" VARCHAR2(50),
"ADDR2" VARCHAR2(50), "CITY" VARCHAR2(25), "STATE" VARCHAR2(25),
"PINCODE" VARCHAR2(6));
( ADDR_NO is primary key )
Problem: I want to apply foreign key constraints on ADDR_DTLS table so that Before inserting value in ADDR_DTLS table it must check, VALUE in ADDR_DTLS.CODE_NO must be PRESENT either in attribute value CUST_MSTR.CODE_NO or EMP_MSTR.CODE_NO or NOMINEE_MSTR.CODE_NO table .
I applied the foreign key constraints using this syntax
CREATE TABLE "DBA_BANKSYS"."ADDR_DTLS"("ADDR_NO" NUMBER(6),
"CODE_NO" VARCHAR2(10),      "ADDR_TYPE" VARCHAR2(1), "ADDR1" VARCHAR2(50),
"ADDR2" VARCHAR2(50), "CITY" VARCHAR2(25), "STATE" VARCHAR2(25),
"PINCODE" VARCHAR2(6),
constraints fk_add foreign key CODE_NO references CUST_MSTR. CODE_NO,
constraints fk_add1 foreign key CODE_NO references EMP_MSTR. CODE_NO,
constraints fk_add2 foreign key CODE_NO references NOMINEE_MSTR.CODE_NO);
(foreign key)
ADDR_DTLS.CODE_NO ->CUST_MSTR.CUST_NO
ADDR_DTLS.CODE_NO ->NOMINEE_MSTR.NOMINEE_NO
ADDR_DTLS.CODE_NO ->BRANCH_MSTR.BRANCH_NO
ADDR_DTLS.CODE_NO ->EMP_MSTR.EMP_NO
When I applied foreign key constraints this way, its gives a error called foreign key constraints violation. (I understand that, its searches the attribute value of ADDR_DTLS.CODE_NO in all the three tables must be present then the value will be inserted. But I want, if the value is in any of the three table then its should insert the value or its gives an error.)
Please help me out, though i put the question and i want too know how to apply the forign key in this way. and is there any other option if foreign key implementation is not pssible.

If you are on 11g you can use ON DELETE SET NULL:
CREATE TABLE addr_dtls
( addr_no          NUMBER(6) CONSTRAINT addr_pk PRIMARY KEY
, addr_cust_no     CONSTRAINT addr_cust_fk    REFERENCES cust_mstr    ON DELETE SET NULL
, addr_emp_no      CONSTRAINT addr_emp_fk     REFERENCES emp_mstr     ON DELETE SET NULL
, addr_nominee_no CONSTRAINT addr_nominee_fk REFERENCES nominee_mstr ON DELETE SET NULL
, addr_type        VARCHAR2(1)
, addr1            VARCHAR2(50)
, addr2            VARCHAR2(50)
, city             VARCHAR2(25)
, state            VARCHAR2(25)
, pincode          VARCHAR2(6) );In earlier versions you'll need to code some application logic to do something similar when a parent row is deleted, as otherwise the only options are to delete the dependent rows or raise an error.
btw table names can be up to 30 characters and don't need to end with MSTR or DTLS, so for example CUSTOMERS and ADDRESSES might be more readable than CUST_MSTR and ADDR_DTLS. Also if the Customer/Employee/Nominee PKs are generated from a sequence they should be numeric.
Edited by: William Robertson on Aug 15, 2010 6:47 PM

Import table data in right order to avoid violating foreign key constraints

Gentlemen
I am trying to import table data into an existing 10g schema using datapump import in table mode.
However, in order to avoid violating foreign key constraints, the tables must be loaded in a specified order. I tried specifying the order in the TABLES parameter:
TABLES=table1,table2,table3 etc.
However, datapump seems to chose its own order leading to errors like the following:
ORA-31693: Table data object "SCHEMAX"."TABLE3" failed to load/unload and is being skipped due to error:
ORA-02291: integrity constraint (SCHEMAX.TABLE3_TABLE1#FK) violated - parent key not found
I want to try to avoid having to disable all foreign keys because there are hundreds of them.
Any advice?
Yours
Claus Jacobsen, Denmark

Thanks Anantha.
Since I am only loadding data (the constraints are already defined in the target database), I am not sure whether this approach would work. Meanwhile I have solved the problem of moving data from one system to another using another, tedious and far from elegant approach that I would prefer to not eloborate on:-)
However, I have also discovered another probable reason why the foreign key constraints were violated, other than wrong order of table data loading. It turns out almost every single table in the schema contains a trigger supposed to generate a unique row ID from a sequence on insert such as:
CREATE OR REPLACE TRIGGER "SCHEMAX"."TABLEX#B_I_R"
BEFORE INSERT
ON TABLEX
FOR EACH ROW
DECLARE
BEGIN
SELECT tablex_seq.nextval INTO :NEW.ID FROM dual;
END;
If the import mechanism fires this trigger, and the sequences in the source and the target systems are not synchronized, then I guess that referred records a more than likely to end up with wrong ID's compared to the row ID's in the referring rows?
Spooky. Anybody can confirm this theory?
Yours
Claus
Message was edited by:
user586249

Generated Script fails when attempting to drop Foreign Key Constraint

I made some changes to my database. I used the generate script process to generate a drop and create script to these tables. The generated script first ran Alter Table Drop Constraints to drop the Foreign Key constraints and then did Drop tables
and then did create table to construct the script with the proper changes.
However, when we attempted to run the script, all of the Drop constraint statements failed reporting that there was no such constraint. Then the drop table scripts failed because of the existence of the very foreign key constraints that SQL Server
had just stated did not exist.
BOL states that the statement "DROP { [ CONSTRAINT ] constraint_name | COLUMN column_name } " is "Used in a CHECK, FOREIGN KEY, UNIQUE, or PRIMARY KEY constraint." So why couldn't I drop those specified Foreign
Key constraints in a script generated by SQL Server itself.
Edward R. Joell MCSD MCDBA

Are you sure there are no Constraints on other tables which are causing your issue?
If a foreign key from table abc refences table def it will cause the drop to fail.
If your script is already attempting to drop such constraints, have you checked that they are dropping from the correct table (and not the table that would be the target of the drop)?
I discovered two things yesterday and one thing today about generated scripts.
When you generated a script to drop and create a set of tables and you mark it to include foreign keys, the generated script will first create a set a scripts to drop the foreign keys , then will create a set of statements for each table that will,
first, again drop the same foreign keys that it did earlier, then drop the table. If there is no "if exists" statement for each statement, the drop constraint will fail.
The script generated by the generate scripts wizard, even when you set the Drop and Create option in the advanced tab, unlike the scripts generated when you right click a table and select Drop and Create from the context menu, does not by default create
an "If Exists" statement before the attempt to drop anything.
You can make the generate Scripts wizard generate an "if exists" statement by changing the "Include if NOT EXISTS" option on the advanced tab to true. However, while the script generator will find all of the foreign keys that show that
table as the parent_id, it will not show the FK constraints on tables which are not being dropped and created. Nor can you find them by querying the sys.foreign_keys view using the standard type of Foreign Key "If Exists" statement because
it would do a query like
SELECT *
FROM sys.foreign_keys
WHERE object_id = OBJECT_ID(N'[dbo].[FK_prc_ContractSubLines_prc_PRSubLines]')
AND parent_object_id = OBJECT_ID(N'[dbo].[prc_ContractSubLines]')
And the script generator does not care even if you show an option like "Generate Scripts For Dependent Objects", it will not generate a drop script for the foreign constraints on other tables that reference your table. I have not even found
a way to get back the results of a query on the sys.foreign_keys view that will show those keys that reference your table. The only thing I been able to do is to open the table in design and check out the list of relationships in your table and see open each
relationship and see which table is the "foreign key table" rather than the primary key table. This will make writing drop and create scripts very very long and tedious. As you would have to create addional Alter tables scripts to do a drop
and create foreign keys on each table referencing yours and manually place them into your scripts at correct locations. This is almost as bad as the Oracle SQL Developer's generate script results which (at least in 2010) so screws up the order of the generated
script that it is trying to create foreign keys on tables it has not created yet.
So Patrick I see that you thought about the foreign keys on other tables. I wish I had read your post before spending the morning troubleshooting this issue based on this morning's script that ran and crashed embarrassingly.
I would like to know if someone has a query to reveal all of the foreign keys that reference your table from another table using the sys views. As it is I have to open each table in design to get a list of FKs that reference it.
Edward R. Joell MCSD MCDBA

Creating a foreign key constraint on a synonym of table in another schema.

Hi,
I am having two user operapps and oper
owner of table po_vendors is operapps ,i have created a synonym in oper with select permission.
now i am trying to create a foreign key.
ALTER TABLE OPS_BR_VENDORS ADD ( FOREIGN KEY (VENDOR_ID) REFERENCES PO_VENDORS (VENDOR_ID));
the bolded po_vendors is the synonym for the table po_vendors in operapps.
i am getting the below error message.
SQL> ALTER TABLE OPS_BR_VENDORS ADD ( FOREIGN KEY (VENDOR_ID) REFERENCES PO_VENDORS (VENDOR_ID));
ALTER TABLE OPS_BR_VENDORS ADD ( FOREIGN KEY (VENDOR_ID) REFERENCES PO_VENDORS (VENDOR_ID))
ERROR at line 1:
ORA-01031: insufficient privileges.
i have given dba privileges to oper user.
Please advice.

1) You cannot create a constraint on a synonym. You have to specify a physical table (i.e. OPERAPPS.PO_VENDORS)
2) The owner of the OPS_BR_VENDORS table will need to have the REFERENCES permission on the PO_VENDORS table granted directly (not via a role).
Justin

Query the name of the parent table in a foreign key constraint

Hello,
Does anyone know how to query for the parent table name in a foreign key constraint? I don't see that relationship in ALL_CONS_COLUMNS or ALL_CONSTRAINTS.
Thanks in advance,
Michael

or try this...
SELECT rc.TABLE_NAME "PK_Table_Name",cc.TABLE_NAME "FK_Table_Name",
       case when cc.column_name = rc.column_name
            then c.TABLE_NAME || '(' || cc.COLUMN_NAME || ')'
            else r.TABLE_NAME || '(' || rc.COLUMN_NAME || ') = ' ||c.TABLE_NAME || '(' || cc.COLUMN_NAME || ')' end as "TABLE_NAME(COLUMN_NAME)"
from all_constraints c,
     all_constraints r,
     all_cons_columns cc,
     all_cons_columns rc
WHERE
     r.table_name = upper('emp')
and      c.CONSTRAINT_TYPE = 'R'
and     c.R_OWNER = r.OWNER
and     c.R_CONSTRAINT_NAME = r.CONSTRAINT_NAME
and     c.CONSTRAINT_NAME = cc.CONSTRAINT_NAME
and     c.OWNER = cc.OWNER
and     r.CONSTRAINT_NAME = rc.CONSTRAINT_NAME
and     r.OWNER = rc.OWNER
and     cc.POSITION = rc.POSITION
ORDER BY r.TABLE_NAME;

Primary Key and Foreign Key Constraints

Hi All,
I would like to know PRIMARY KEY and FOREIGN KEY constraints on existing oracle tables. Could any one suggest me how to find out.
Thanks,
RED

You can query DBA_CONSTRAINTS to get a list of all the constraints on table A and/or table B. The documentation I linked to gives a full list of the data you can see in DBA_CONSTRAINTS, but it includes things like the referenced table name and referenced constraint name for a foreign key constraint. If A is a parent of B or B is a parent of A, you could match up the parent's primary key constraint to the child's foreign key constraint.
More generally, though, if you don't know that one of the tables is a parent of the other, figuring out how to join the two tables is probably not something that can be done using just the Oracle data dictionary. You would probably need an understanding of the data model being used to figure out what intermediate table(s) needed to be joined in order to relate rows in A to rows in B.
Justin

Oracle 9i primary and foreign key constraint

I had created table in the following way
create table dept(deptno number,dname varchar2(20));
create table emp(empno number primary key,ename varchar2(25), deptno number references dept(deptno));
One can get constraint name and constraint type from user_constraints table. But I want to know name of the column of table from which column is used as foreign key in another table. How to get such information?

SQL> Select *From user_cons_columns A
2   Where Constraint_Name In (Select r_Constraint_Name
3                           From User_Constraints B
4        Where Table_Name='EMP'
5          And Constraint_Type='R'
6          Group By r_Constraint_Name
7          )
8 /
OWNER                          CONSTRAINT_NAME                TABLE_NAME                     COLUMN_NAME
SCOTT                          PK_DEPTNO                      DEPT                           DEPTNO                             Edited by: babaravi on Oct 5, 2009 3:34 PM

Foreign Key Constraint Failure on Self-Referencing Table

In a recent data deletion project, I ran into a problem where Oracle allowed for a record (the parent) to be deleted when there still existed a child record in the same table which referred to the parent.
An abbreviated version of the table is as follows:
create table test (
template_id number not null,
customer_id number null,
parent_id number null,
constraint pk_test primary key (template_id),
constraint r_parent foreign key (parent_id) references test (template_id));
The parent and child records are as follows:
Parent: template_id = 100, customer_id = 200, parent_id = null
Child: template_id = 101, customer_id = null, parent_id = 100
Records were deleted from this table using:
DELETE FROM test WHERE customer_id = 200;
When this statement is executed, is it being executed as part of 155 delete statements using PL/SQL, and tens of thousands of records from 155 tables are being deleted. These delete statements have been ordered taking into account foreign key constraints. All 155 statements are being deleted in a single transaction. The delete statement above was the 23rd statement of the set to be executed. I would have expected when this delete statement was executed, an error would have been thrown. However, all 155 delete statements successfully complete, and after committing the results, the child record above still exists in the DB as an orphan. I also tried executing the first 23 statements manually in SQL*Plus (still one transaction), and the problem still occurs: the parent is deleted and the child is orphaned.
If I execute the very simple example above, I do indeed get an referential constraint error.
Has anyone ever encountered this situation? And does anyone have any ideas how to go about troubleshooting this problem. We need to know the cause of this, as we have a small handful of table with a similar self-referential foreign key constraint set-up.
Thank you very much in advance,
Mark

First of all, the very simple example that I outlined above I have already tried and it worked: when I attempted to delete the parent a referential integrity error was thrown as one would expect. This small example was my test case to see if I could reproduce what I'm seeing in our application in a more manageable and demonstrable example. But as it worked, I'm still perplexed in reconciling the differences between what I'm seeing in our application (which I can't demonstrate in this help group) and the test case. When I used the test case in my first posting in this thread, I used it to help describe the problem I'm encountered, even though that small example works.
Below is more of the table you've asked for.
OWNER           CONSTRAINT_NAME          CONSTRAINT_TYPE     TABLE_NAME     SEARCH_CONDITION     R_OWNER            R_CONSTRAINT_NAME     DELETE_RULE     STATUS          DEFERRABLE            DEFERRED         VALIDATED     GENERATED     BAD     RELY     LAST_CHANGE           INDEX_OWNER INDEX_NAME       INVALID     VIEW_RELATED
"DOCPADMIN"     "R_TEMPLATE_PARENT"     "R"             "DCR_TEMPLATE"      (null)                  "DOCPADMIN"     "XPKDCR_TEMPLATE"     "NO ACTION" "ENABLED"   "NOT DEFERRABLE"    "IMMEDIATE" "VALIDATED"      "USER NAME"     (null)     (null)     "2010-01-13 19:01:21"     (null)        (null)         (null)       (null)
"DOCPADMIN"     "XPKDCR_TEMPLATE"       "P"             "DCR_TEMPLATE"      (null)                       (null)     (null)                      (null)          "ENABLED"     "NOT DEFERRABLE"    "IMMEDIATE"      "VALIDATED"     "USER NAME"     (null)     (null)     "2010-01-13 15:48:31"     (null)     "XPKDCR_TEMPLATE"   (null)     (null)Overall, I haven't said that Oracle's FK mechanism is broken. What I've said is that I've got a situation that I'm trying to understand. My first attempt at my test case didn't work because the test case worked as it should. I'm trying to figure out another course of action to try and figure this situation out.

Delete a user from a table whose name is a foreign key in other tables

Dear All;
I am trying to figure out an easy way to do this. I just recently took someone application who utilized 500 tables. I am trying to delete a user from a table called member_table. However, I am having problems doing so because the user name is a foreign key in other tables which has a relationship with this member_table. I really can't naviagte through all 500 different tables and start deleting the user from each table . hence, I would like to figure out a way to delete the user from the member_table without getting the error message
ORA - 02292 "Integrity Constraint (....) violated child record found

Unless you want to find and re-create all of the FK's that point to that field so you can make them ON DELETE CASCADE (note it is the FK not the PK that has that attribute), you will need to either delete that member id from each of the child tables individually or update each one individually to either null or some valid value in member_table before you can delete the id from member_table.
You can find all of the tables, and the corresponding column_name that have an FK relationship to memeber_table with the following:
SELECT c.table_name, col.column_name
FROM user_constraints c, user_cons_columns col
WHERE c.constraint_name = col.constraint_name and
      c.r_constraint_name = (SELECT constraint_name
                             FROM user_constraints
                             WHERE table_name = 'MEMBER_TABLE' and
                                   constraint_type = 'P') and
     c.constraint_type = 'R';If there are a lot of these, you could use something similar to generate the set of delete/update statements that would be needed.
John

Publish: dropping index when it is used for foreign key constraint enforcement

Hi,
I'm trying to update a target schema from a reference database via Publish. Among the changes to apply, there's an index that needs to be dropped. Since it's linked to a foreign key constraint, it cannot be deleted unless the foreign key is temporarily dropped
(I saw somewhere that disabling the foreign key should be enough but it doesn't seem to work either).
Since there are other changes to be made on the same table, this foreign key also has to be dropped before the script can delete the table and re-create it. This part of the script is correctly generated. The problem is that this part appears after the 'DROP
INDEX' instruction.
So when generating the update script, SSDT tries to drop the index BEFORE dropping the foreign key. And I can't drop the foreign key in my custom pre-deployment script, otherwise the update script would fail when trying to delete it again.
Shouldn't SSDT be smart enough to drop the constraint before the index? Is it a bug or did I forget to set an option? If it's not a bug, what can I do apart from doing it manually?
Thank you for your help

Hi Elsa,
That sounds like a bug. Could you please file a Connect issue for this at
https://connect.microsoft.com/SQLServer/feedback/CreateFeedback.aspx using the category "Developer Tools (SSDT, BIDS, etc.)"? We're trying to track all bugs through
Connect so that you can tell when we have fixed the issue and we can request more information.
A workaround for this issue might be to write a pre-deployment script for your project to drop the foreign key prior to deployment. A pre-deployment script can be added to your project by right-clicking on the
project in solution explorer and then clicking on Add > Script... and selecting Pre-Deployment Script from the list.
Thanks!

How to alter or add foreign key constr to table having child rows or data

Hi,
I have a table by name DEPT in which the column DEPTNO is a primary key column and have data in it for all the columns . Now I have a EMP table where in the column DEPTNO is not having any constraint including foreign key constraint too. Now i have data in the EMP table for all the columns . now i would like to add the foreign key constraint to DEPTNO column in the EMP table referencing the DEPTNO column in the DEPT table. Both the table do not have any null values .
I need to add the foreign key without deleting the data in the EMP table.
Please advice.
Regards,
Vinesh

Hi,
I need to add the foreign key without deleting the data in the EMP table.Foreign key constraint can have only those values which are present in the primary key of the parent table or null.
When your tables are populated with values and then you are adding the constraint then,
the parent table data is only present in child table or null values.
Example
SQL> create table emp_bkp as select * from emp;
Table created.
SQL> create table dept_bkp as select * from dept;
Table created.
SQL> alter table dept_bkp
2 add constraint pk_deptno primary key(deptno);
Table altered.
SQL> select distinct deptno from emp_bkp;
    DEPTNO
        30
        20
        40
        10
SQL> select deptno from dept_bkp;
    DEPTNO
        10
        20
        30
        40
        55
SQL> alter table emp_bkp
2   add constraint fk_deptno_bkp foreign key(deptno)
3    references dept_bkp(deptno);
Table altered.
SQL> alter table emp_bkp
2 drop constraint fk_deptno_bkp;
Table altered.
SQL> insert into emp_bkp(empno,ename,deptno) values(142,'Fenny',90);
1 row created.
SQL> alter table emp_bkp
2 add constraint fk_deptno_bkp foreign key(deptno)
3   references dept_bkp(deptno);
add constraint fk_deptno_bkp foreign key(deptno)
ERROR at line 2:
ORA-02298: cannot validate (SCOTT.FK_DEPTNO_BKP) - parent keys not found
SQL> update emp_bkp
2 set deptno=null
3 where empno=142;
1 row updated.
SQL> alter table emp_bkp
2 add constraint fk_deptno_bkp foreign key(deptno)
3   references dept_bkp(deptno);
Table altered.
SQL> insert into dept_bkp (deptno,dname)values(90,'IT');
1 row created.
SQL> update emp_bkp
2 set deptno=90
3 where empno=142;
1 row updated.Twinkle

Foreign key constraint on multi-column primary key accepts 1 empty column!?

Hi, we have a reference table with a two-column primary key. In the child table there is a non-mandatory foreign key constraint to this table. So if both child columns are null it's ok too. But now we see that if one of the two child table columns that build up the foreign key is null, the other column can have any (non-existant in the master-tabel) value you like!? That does not make sense.
Can anyone explain this to me???
Regards, Paul.

Paul, I believe that this is in accordance to the ANSI SQL standard requirement for the treatment of nulls in a multi-column FK. In any case Oracle specifically states this is the way FK work From the 10 Concepts manual, Ch 21 Data Integrity, topic Nulls and Foreign Keys:
The relational model permits the value of foreign keys either to match the referenced primary or unique key value, or be null. If any column of a composite foreign key is null, then the non-null portions of the key do not have to match any corresponding portion of a parent key. <<HTH -- Mark D Powell --

FOREIGN KEY Constraint And Table Lock

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