Is a foreign key MUST have a UNIQUE or PK column as a reference?

Similar Questions

• Two foreign keys of a table in a single column

  Hi gurus

  I wonder that can we add two foreign keys of a table on a single column, I think the answer is, but what should be the reason behind this?

  Appreciate if someone there explain to me...

  Concerning

  Muzz

  Hello Muzz,

  Perhaps the example of human Chen reveals a design error.
  If a student has a 'teacher_id' "teacher" FK and FK for "emp" becaue each teacher is an EMP, I guess that the correct design would be to have only the FK of 'teacher' and to have another pointing to the 'emp' table in the 'teacher' tabe FK

  But we can imagine comical situations...
  CREATE TABLE PEOPLE (id NUMBER of KEY PRIMARY, name VARCHAR2 (20 CHAR),...);
  CREATE TABLE SCIENTIST (id people KEY PRIMARY NUMBER (id) REFERENCES, discipline VARCHAR2 (20 CHAR),...);
  CREATE TABLE POLICEMAN (id REFERENCES to KEY PRIMARY NUMBER (id), hire_date people DATE,...);

  First table = all.
  2nd: a subset of the first, with people having the profile of 'scientific '...
  3rd: a subset of the first, with people being a policeman.
  It might be people first table and in none of the 2nd and 3rd, 1st and 2nd, 1st and 3rd only or in the 3 tables.

  Then we can have a fourth table of 'something' referring to a person who must be a scientist and a police officer.

  Here is a sqlplus session illustrating; the last piece: I try inserting several lines in xxxx, only the last is accepted.

  SQL > CREATE TABLE PEOPLE (id NUMBER of the PRIMARY KEY, name VARCHAR2 (20 CHAR));
  Table created.

  SQL > CREATE TABLE SCIENTIST (people of REFERENCES of KEY PRIMARY NUMBER id (id), discipline VARCHAR2 (20 CHAR));
  Table created.

  SQL > CREATE TABLE POLICEMAN (people of REFERENCES of KEY PRIMARY NUMBER id (id), DATE hire_date);
  Table created.

  SQL > CREATE TABLE XXXX (id PRIMARY KEY NUMBER, people_id NUMBER, any other VARCHAR2 (30 CHAR));
  Table created.

  SQL > ALTER TABLE ADD CONSTRAiNT fk_xxsci FOREIGN KEY (people_id) scientific xxxx REFERENCES (id);
  Modified table.

  SQL > ALTER TABLE ADD CONSTRAiNT fk_xxpol FOREIGN KEY (people_id) police xxxx REFERENCES (id);
  Modified table.

  SQL > INSERT INTO person VALUES (100, 'John');
  1 line of creation.

  SQL > INSERT INTO person VALUES (120, 'Mary');
  1 line of creation.

  SQL > INSERT INTO person VALUES (103, 'Tom');
  1 line of creation.

  SQL > INSERT INTO person VALUES (123, "Bruno");
  1 line of creation.

  SQL > INSERT INTO VALUES of scientific (120, 'Chemistry');
  1 line of creation.

  SQL > INSERT INTO scientific VALUES (123, 'Mathematics');
  1 line of creation.

  SQL > INSERT INTO VALUES of policeman (103, DATE ' 2001-04-01');
  1 line of creation.

  SQL > INSERT INTO VALUES of policeman (123, DATE ' 1998-07-01');
  1 line of creation.

  SQL > INSERT INTO xxxx VALUES (1, 456, "nothing");
  ERROR on line 1:
  ORA-02291: integrity constraint (SYS. FK_XXPOL) violated - key parent not found

  SQL > INSERT INTO xxxx VALUES (1, 100, "only to people");
  ORA-02291: integrity constraint (SYS. FK_XXPOL) violated - key parent not found

  SQL > INSERT INTO xxxx VALUES (1, 120, "only the learned");
  ORA-02291: integrity constraint (SYS. FK_XXPOL) violated - key parent not found

  SQL > INSERT INTO xxxx VALUES (1, 103, "only police officer");
  ORA-02291: integrity constraint (SYS. FK_XXSCI) violated - key parent not found

  SQL > INSERT INTO xxxx VALUES (1, 123, 'ok');
  1 line of creation.

  Best regards

  Bruno Vroman.

• foreign key mapped to a unique constraint

  OK, here's the question
  
  create a parent of the table (col1, col2 char char);
  alter table add constraint pk_parent key (col1) parent primary;
  alter table add constraint uk_parent unique(col1,col2) parent;
  
  Insert into parent values ('A', '7');
  
  * 1 row created.*
  
  create the child table (col1, col2 char char);
  ALTER table child add constraint fk_child_parent foreign key(col1,col2) references parent(col1,col2);
  
  insert into values('B','4') of the child;
  
  insert into the child values('B','4')
  ***
  ERROR on line 1:
  ORA-02291: integrity constraint (WILDGOD. FK_CHILD_PARENT) violated - parent key
  not found
  
  That's what I expect... but
  
  insert into values('B',) of the child;
  
  * 1 row created.*
  
  
  why he let me do, I realize its because col2 is NULL, but it should not yet check for col1 in the parent?
  
  Please clarify, thanks in advance.

  Documented behavior.

  See here:
  http://download.Oracle.com/docs/CD/E11882_01/AppDev.112/e10471/adfns_constraints.htm#ADFNS273

  -Mark

• another computer on the network is using the same IP address that your computer uses. Each computer on a network must have a unique IP address. To resolve this problem, run Network Diagnostics

  another computer on the network is using the same IP address that your computer uses.

  Hi johnnyredd

  
  1. is connected to a domain or a server computer?
  2. what operating system is installed on the computer?

   

  You can refer to the link below and check if the information provided will help you-

  http://Windows.Microsoft.com/en-us/Windows7/get-help-with-there-is-an-IP-address-conflict-message

   

  Check out the link below to identify the operating system installed.
  http://Windows.Microsoft.com/en-us/Windows7/help/which-version-of-the-Windows-operating-system-am-i-running

   

  I hope this helps.

• Details of the foreign key constraints

  Why foreign key constraints is not ongoing validation in case of null values?
  For example, in the table EMP and DEPT table, EMP. References DEPTNO Dept. DEPTNO.
  But I am able to insert rows into the EMP table that contains nulls for EMP. DEPTNO.

  Prasath N wrote:
  Why foreign key constraints is not ongoing validation in case of null values?
  For example, in the table EMP and DEPT table, EMP. References DEPTNO Dept. DEPTNO.
  But I am able to insert rows into the EMP table that contains nulls for EMP. DEPTNO.

  I guess he's saying essentially that a foreign key must have a parent key or can be an orphan. But may not be a key that is not listed in the parent.

  And also NULL is neither equal to anything, nor does not correspond to something.

  But still, you can put a NOT NULL constraint if you do not want your foreign key to contain orphaned records.

• foreign key index

  I read a book on the index, he said
  

  You should almost always index foreign keys because they are frequently used in joins. In addition, if you intend to delete or update unique or primary keys on the parent table, you should index the foreign keys to improve the locking of child records.

  what I don't understand, I should create index on the foreign key in parent-child table or table column or both?
  
  Thank you

  Hello

  806540 wrote:
  I read a book on the index, he said

  You should almost always index foreign keys because they are frequently used in joins. In addition, if you intend to delete or update unique or primary keys on the parent table, you should index the foreign keys to improve the locking of child records.
  

  what I don't understand, I should create index on the foreign key in parent-child table or table column or both?

  They mean that you need to create an index in the child table, that is the table that contains the foreign key constraint.

  In order to have a foreign key constraint, it must have a primary key constraint, or a unique constraint on the column, or columns referenced in the parent table. Either type (primary key or unique) automatically creates an index, so there is nothing more you need to do in the parent table.

• Drop partition without disabling the foreign key

  Hi all
  
  I have a table parent and child.
  
  Parent table
  
  create the table parent_1
  (identification number,
  create_date date,
  Constraint parent_1_pk001 PRIMARY KEY (id))
  PARTITION OF RANGE (create_date)
  INTERVAL (NUMTODSINTERVAL(1,'DAY'))
  (PARTITION parent_1_part VALUES LESS THAN (January 1, 2010 '));
  
  Child table
  create the table child_1
  (identification number,
  create_date date,
  Constraint child_1_fk001 FOREIGN KEY (id)
  REFERENCES parent_1 (id))
  PARTITION OF RANGE (create_date)
  INTERVAL (NUMTODSINTERVAL(1,'DAY'))
  (PARTITION create_date_part VALUES LESS THAN (January 1, 2010 '));
  
  
  I have problems to delete partition.
  Parent_1
  1 JULY 26, 12
  2 JULY 26, 12
  
  Child_1
  1 JULY 26, 12
  
  ALTER drop partition table CHILD_1 SYS_P274;
  table altered CHILD_1.
  
  ON THE PARENT PARTITION A FALL
  ALTER drop partition table parent_1 SYS_P273;
  
  Error report:
  SQL error: ORA-02266: unique/primary keys in table referenced by foreign keys enabled
  02266 00000 - "unique/primary keys in table referenced by foreign keys enabled.
  * Cause: An attempt was made to truncate a single table or
  primary keys referenced by foreign keys in another table.
  Other unauthorized trades are a drop/truncate partition a
  partitioned table or an ALTER TABLE EXCHANGE PARTITION.
  * Action: Before performing the operations described above, the table, disable the
  constraints foreign key in other tables. You can see what
  constraints are making reference to a table by issuing the following
  command:
  SELECT * FROM USER_CONSTRAINTS WHERE TABLE_NAME = 'tabnam ';
  
  
  PLEASE KNOW IF THERE IS A WAY TO THE PARENT PARTITION DROP WITHOUT TOGGLE FOREIGN CONSTRAINTS
  
  
  Thank you

  SQL Error: ORA-02266: unique/primary keys in table referenced by enabled foreign keys
  02266. 00000 - "unique/primary keys in table referenced by enabled foreign keys"
  *Cause: An attempt was made to truncate a table with unique or
  primary keys referenced by foreign keys enabled in another table.
  Other operations not allowed are dropping/truncating a partition of a
  partitioned table or an ALTER TABLE EXCHANGE PARTITION.
  *Action: Before performing the above operations the table, disable the
  foreign key constraints in other tables. 
  

  You can do until you disable the foreign key constraint

  http://jonathanlewis.WordPress.com/2006/12/10/drop-parent-partition/

  Hope this helps

  Mohamed Houri
  www.hourim.WordPress.com

• Foreign key problem

  Hi all...
  I'm new to this field of database... I have a small question about the foreign key
  
  I have two table name as ACCT_MSTR column ACCT_NO
  & FD_MSTR another FD_SER_NO column.
  
  Now, I create a table called ACCT_FD_CUST_DTLS
  having the column ACCT_FD_NO, CUST_NO.
  
  Now, I want to do a foreign key relationship are provided with
  acct_mstr & fd_mstr on a single column of acct_fd_cust_dtls (acct_fd_no)
  That is to say.
  foreign key: -.
  ACCT_FD_CUST_DTLS. ACCT_FD_NO-> ACCT_MSTR. ACCT_NO
  OR
  ACCT_FD_CUST_DTLS. ACCT_FD_NO-> FD_MSTR. FD_SER_NO
  
  How can I make this relationship?
  Please help me by providing the syntax
  
  Thanks in advance

  user11207304 wrote:
  @ Sissi
  No, this isn't like that
  values are either present in ACCT_MSTR. ACCT_NO or the FD_MSTR. FD_SER_NO.
  It is not necessary to present the two table.

  Referential constraints do not work like that. If you build a relationship, it must be respected.

  If the value is not found in one of the parents (in this case), there will be an exception.

  IMO, the solution to your problem is not a referential constraint, but a trigger.

• Adding a foreign key when adding a column

  Hi all
  
  How to add a column with constriant foreign key
  
  I have a table TEST (pk number nm)
  and TEST1 (PK nm1)
  
  TEST1, I need to add a column nm2 which referred to TEST (nm), using the unique ALTER command
  
  
  Please help in this.

  Hello

  Please check the documentation for it, it's all there:
  http://download.Oracle.com/docs/CD/B19306_01/server.102/b14200/clauses002.htm#CJAGIICD

  ALTER TABLE test1 ADD (
   nm2 NUMBER
   CONSTRAINT nm2_fk REFERENCES test(nm)
  );
  

• Foreign keys (null)

  Your primary key is not null.
  If the foreign key also have the value null is not*, since it is based on a PK?

  Clive_S wrote:
  Your primary key is not null.
  If the foreign key also have the value null is not*, since it is based on a PK?

  It's all business requirements. If your requirement of bussiness stats this column must not be zero then do else do not.
  It is not mandatory to have a foreign key to null.

  For example:
  A new employee to join the Organization, which the Department (foreign key) has not yet been set.

  Concerning
  Anurag

• Question on foreign key

  Hello
  
  I have a question about foreign key. When we create an index on a foreign key index name are displayed in the column index_name dba_constraints DD.
  
  But the name of the index associated with the primary key is displayed.
  
  Why so much?
  
  Thanks in advance.

  Unique or Primary Key cannot guarantee the uniqueness of a column with an Index on that column. That's why Oracle will create an Index by default if there is no such thing as an index on that column all to utter those two constraints. If an index is always associated with these two constraints.

  But no foreign key guarantees uniqueness on a column. And an Index on a foreign key is not required. So even if you create an index on a foreign key column that index is not associated with the foreign key.

• foreign keys different files randomly

  Hello dear members,
  
  Here is my table
  
  MY_TABLE
  --------------------
  PRIMARY_KEY FOREIGN_KEY
  1A
  1 b
  3A
  4 B
  5 B
  6 B
  8 m
  8 C
  9 C
  10 D
  
  I want to fetch random files N where these records N foreign keys must be different.
  
  Example outouts:
  N = 2
  1
  4
  
  N = 3
  1
  7
  9
  
  
  I'm sure there is a quick and logical way to achieve this goal, but I couldn't find that either by myself or through google.
  Thanks for your replies.

  brkmhr wrote:
  Hello

  Are you sure that's the answer? Because I'm not!

  Stew of solution is really COOL, but your sentence unfortunately does not show satisfaction.

  If you want to try its solution with a slight change, you exactly what you need:

  with mydata AS
  (
     SELECT 1  pk, 'A' fk FROM DUAL UNION ALL
     SELECT 2  pk, 'A' fk FROM DUAL UNION ALL
     SELECT 3  pk, 'A' fk FROM DUAL UNION ALL
     SELECT 4  pk, 'B' fk FROM DUAL UNION ALL
     SELECT 5  pk, 'B' fk FROM DUAL UNION ALL
     SELECT 6  pk, 'B' fk FROM DUAL UNION ALL
     SELECT 7  pk, 'B' fk FROM DUAL UNION ALL
     SELECT 8  pk, 'C' fk FROM DUAL UNION ALL
     SELECT 9  pk, 'C' fk FROM DUAL UNION ALL
     SELECT 10 pk, 'D' fk FROM DUAL
  )
  SELECT pk
    FROM (  SELECT a.*
                 , ROW_NUMBER () OVER (PARTITION BY fk ORDER BY DBMS_RANDOM.random) rn
              FROM mydata a
          ORDER BY fk)
   WHERE rn = 1
     AND ROWNUM <= 3  -- this is your N
  ;
  

  Simply replace the number in the last line of the n you want.

  Next time try the solution before giving these answers.

  Kind regards.
  Al

• Rename the foreign key constraint

  Hello
  
  I have table tbl_a with a column a_col1 SEO tbl_b.b_col1
  
  I want to create the name of the foreign key as FK_A_COL1 constraint which is FK_ < COLUMN NAME OF the CHILD >.
  
  Foreign naming key standards does not have the use of the name of the child under the name column.
  
  Is there any other solution/script to achieve this?
  
  Thank you.

  fkeys = model.getFKIndexAssociationSet().toArray();
  for (var i = 0; i;//also can use fk.getTable().getAbbreviation()fkname = "FK_"+fk.getTable().getName();cols = fk.getColumns();for( var k = 0;k
  

• Can we create a foreign key by using built in functions?

  Hi all

  I'm in the need to create a foreign key referring to an expression of a column in another table.

  For example, I try below and I got some errors.

  CREATE TABLE TABLE_A

  (

  student_id VARCHAR2 (30),

  student_name VARCHAR2 (100),

  CONSTRAINT fk_A FOREIGN KEY (student_id) REFERENCES TABLE_B (UPPER (column_name))

  );

  Please suggest if it is possible that a foreign key could be made in an expression or not?

  2761969 wrote:

  Hi all

  I'm in the need to create a foreign key referring to an expression of a column in another table.

  For example, I try below and I got some errors.

  CREATE TABLE TABLE_A

  (

  student_id VARCHAR2 (30),

  student_name VARCHAR2 (100),

  CONSTRAINT fk_A FOREIGN KEY (student_id) REFERENCES TABLE_B (UPPER (column_name))

  );

  Please suggest if it is possible that a foreign key could be made in an expression or not?

  No - it isn't.

  You can, however, create a VIRTUAL column in the parent table, and then create a foreign key that references.

• correct handling of foreign keys in unique constraints for operations ON DELETE SET NULL

  During my troubleshooting at a client site, I came across an interesting setup where I would like to ask your opinion.

  
  Consider two tables ADTB and TBLB.

  ADTB:

  INT COLA1

  COLA2 INT

  TBLB:

  COLB1 INT

  COLA2 is COLB1 as a foreign key ON DELETE SET NULL value.

  COLA1 and COLA2 are combined into a UNIQUE for the BATTERY constraint.

  I have two records of TBLB:

  (1)

  (2)

  and two DRUM recordings:

  (1, 1)

  (2, 2)

  so far, all the constraints are valid.

  During my research, I learned that I can not put COLA2 null in ADTB for two lines at the same time:

  TBLA UPDATE set COLA2 = NULL where COLA1 = 1;

  -> OK

  TBLA UPDATE set COLA2 = NULL where COLA1 = 2;

  -> VIOLATED UNIQUE CONSTRAINT

  Unfortunately, it's something my application needs, anyway. In order to get this resolved, but I try to understand, what would happen if I:

  REMOVE THE TBLB;

  ?

  It should set COLA2 in ADTB "Null" on the two lines, which is not allowed due to the UNIQUE CONSTRAINT.

  Can someone shed light on this issue? Thank you.

  
  Yours,

  Ronny

  Unfortunately, as you say, you can't not NULL values in such a unique constraint.  It would be the same as if you had a composite primary key and try to allow one of the columns will be null in several rows with the same value in the other column.  NULL is treated as an "unknown" value, it is possible that it could be the same value (it may or may not be, but Oracle does not know), so it must assume that it might be and that's why treat it as if there is the potential for a duplicate... so it's not unique.

  In short, do not allow null values in your unique constraints.

  The default is in the drawing, not in the way that Oracle is the treatment.  Fix the design if you do not have NULL values.

  In terms of relational database design, it seems that you are trying to transform the 1:M relations M:M relations, and which requires an intermediate table if you have M:1 and 1:M between 3 tables instead.