I've been struggling for some time now to figure out a way to create a composite foreign key in liquibase.
I have a table A which has a composite PK, let's say (id1, id2). I'm trying to make another table B, in which the A.PK is mapped as a FK.
I'm using liquibase with YAML and something doesn't seem to add up.
I've tried adding the FK when creating the table (so in the column tag)
- column:
name: id1_id2
type: int
constraints:
nullable: false
foreignKeyName: fk_id1_id2
references: A(id1, id2)
Unfortunately this syntax returns an error:
Caused by: java.sql.SQLSyntaxErrorException: ORA-02256: number of referencing columns must match referenced columns
Another thing that I've tried is creating the table first, with the column for the desired FK and try to add a FK constraint on that column. This doesn't throw any error but it does nothing (also the log for LB says "empty" in the description)
changes:
- addForeignKeyContraint:
baseColumnNames: id1, id2
baseTableName: B
constraintName: fb_id1_id2
referencedColumnNames: id1, id2
referencedTableName: A
Any help would be much appreciated.
Thanks
Have you tried addForeignKeyConstraint? Something like this:
- changeSet:
id: 1
author: you
changes:
- addForeignKeyConstraint:
baseColumnNames: id1, id2
baseTableName: tableB
constraintName: FK_tableB_tableA
referencedColumnNames: id1, id2
referencedTableName: tableA
I don't use Liquibase, but here's how it is supposed to look like, as far as Oracle is concerned: if you want to create a composite foreign key (in the detail table), then it has to reference a composite primary key (in the master table).
Have a look at this example:
SQL> create table master
2 (id_1 number,
3 id_2 number,
4 constraint pk_mas primary key (id_1, id_2));
Table created.
SQL> create table detail
2 (id_det number constraint pk_det primary key,
3 --
4 id_1 number,
5 id_2 number,
6 constraint fk_det_mas foreign key (id_1, id_2) references master (id_1, id_2));
Table created.
SQL>
It just wouldn't work otherwise; that's why you got the error
ORA-02256: number of referencing columns must match referenced columns
because your detail table contained a single column (id1_id2) and tried to reference two columns in table A (id1, id2).
Related
currently i am facing an oracle constraints issue.
After submiting an insert my foreign key constraint(s) won't fire. What it should do is giving two tables the same ID, but unfortunately only the one table with the primary Key is giving an ID. The column with the foreign key in the second table remains null.
For Instance: Insert into table t1 (t1_id,name, dpt) values (value1 (trigger with autoincrement for id), value2, value3); The same procedure is behind table 2, table 3 ... All constraints are written correctly
Table 1 (Emp)
ID Name Department
1 Joe HR
Table 2 (Projects)
ID Project EmpID
1 new (null) -> must be 1
Thank you in advanced.
Constraint: ALTER TABLE "PROJECTS" ADD CONSTRAINT "EMP_FK" FOREIGN KEY ("EMP_ID")
REFERENCES "EMP" ("EMP_ID") ON DELETE CASCADE ENABLE
Trigger: create or replace TRIGGER Projects_TRG BEFORE
INSERT ON Projects FOR EACH ROW BEGIN :NEW.Project_ID := Projects_SEQ.NEXTVAL;
END;
How do i manage to populate the parent id from the parent table into the child table?
Please note that I used different names in my application.
It appears that you've misunderstood the purpose of a foreign key constraint. A foreign key constraint does NOT automatically propagate constraint values from the parent table to the child table. The purpose of the constraint is to ensure that the values of the key column in the child table, when populated, have matching values in the key column of the parent table. Your application is responsible for ensuring that the key column on the child table is populated with the appropriate value. The constraint doesn't do that for you. It's also perfectly legitimate to have a NULL in the key column of the child table, assuming the the column on the child table doesn't have a NOT NULL constraint on it.
I have a problem like
Table A:
-- TableBCId
Table B:
-- Id
Table C:
-- Id
I am looking for a way to create a foreign key table A where an entry can be either in table B or table C
Example entries:
Table A:
-- TableBCId: 1
-- TableBCId: 2
Table B:
-- Id: 1
Table C:
-- Id: 2
I want to avoid if possible:
- Two columns in table A
- Default values
- Additional tables
- Creation of an base entity is not possible
Every idea welcome
The normal way to implement this requirement is with 2 columns, 2 foreign key constraints, and a check constraint to ensure exactly of of the columns populated (if this is a requirement):
create table a
( ...
, b_id references b
, c_id references c
, constraint <name> check ( (b_id is null and c_id is not null)
or (b_id is not null and c_id is null)
)
);
You could, if it helps your UI, create a view over that table that combines B_ID and C_ID into a single column.
But you have said you don't want 2 columns, why is that?
The reason why this is hard is because the data model is wrong. A foreign key references only one table. A table can have more than one foreign key but each is separate. Apart from anything else, how would you know whether bc_id referenced b.id or c.id?
One explanation for this scenario is that table A should really be two tables, BA referencing B and CA referencing C. Alternatively A should reference a super-type table, of which B and C are sub-types. Without knowing the actual business domain it's hard to be sure.
Anyway, the path of least change is two columns.
You can use a insert/update trigger on your Table_A.
Maybe something like this:
CREATE TRIGGER Table_a_trgr
BEFORE INSERT OR UPDATE
on Table_a
FOR EACH ROW
DECLARE
c_row NUMBER;
BEGIN
SELECT count(*)
INTO c_row
FROM (
SELECT ID FROM table_b WHERE id = :NEW.TableBCId
UNION ALL
SELECT ID FROM table_c WHERE İd = :NEW.TableBCId
)
;
IF c_row < 2 THEN
raise_application_error(-20000, 'Error, Foreign Key');
END IF;
END;
/
If you don't want to make a new column in table A.
Then you can make a parent table to B and C.
tableBC:
id
And then create a 1-1 relation with tables B and C to table BC.
tableB:
id,
parent -- 1-1 foreign key to tableBC
tableC:
id,
parent -- 1-1 foreign key to tableBC
Now, in table A
tableA:
id,
TableBCId -- foreign key to tableBC
We have solved a similar problem using this approach.
I have a table and this table has relationship with itself as many-to-many. So i am create another table (second table) that stores two id for composite primary key which comes from original (first) table. But if in second table there is id1=1 and id2=2, then second table shouldn't have id1=2 and id2=1.
So how can i do that, should i write a trigger for that or is there a simple way for oracle.
I use Oracle11g and pl/sql developer.
You can try defining a unique function-based index that automatically defines the index in numerical order. This would ensure that only one of the 2 combinations is ever allowed. Something like:
create unique index your_index on your_table(
least(id1, id2),
greatest(id1, id2)
);
If it matters, there is a slight difference between this approach and MT0's answer that uses the check constraint.
With the check constraint approach, only (id1=1, id2=2) is valid.
With the function-based index approach, both (id1=1, id2=2) and (id1=2, id2=1) are valid, but they can't both be present in the table at any given time.
CREATE TABLE table_name (
id INT PRIMARY KEY
);
CREATE TABLE table_name_many_to_many(
id1 INT REFERENCES table_name( id ),
id2 INT REFERENCES table_name( id ),
CONSTRAINT tnmtm__id1__id2__pk PRIMARY KEY ( id1, id2 ),
CONSTRAINT tnmtm__id1__id2__chk CHECK ( id1 <= id2 )
);
I have a table with three columns, [Id,QTY,Date]. out of these three, two columns [id and date], should be set as primary keys, because I need to fetch the record one by one, from this table, into a reference.
the data to be inserted into this table is
101,10,NULL
101,20,201220
101,7,201440
102,5,null
102,8,201352
date is in yyyyww format
How do I define two columns as composite primary keys when they have null values, duplicates?
alter table abc add constraint pk primary key (ID, DATE);
if I try to alter the table the error appears
Error report:
SQL Error: ORA-01449: column contains NULL values; cannot alter to NOT NULL
01449. 00000 - "column contains NULL values; cannot alter to NOT NULL"
*Cause:
*Action:
Using table level constraint, you can use this query
alter table your_table add constraint pkc_Name primary key (column1, column2)
but first you need to declare the columns NOT NULL. All parts of a primary key need to be NOT NULL.
The column name of your table is ID and it is still null and non-unique, how is it possible. If it is primary key of other table try adding a surrogate key column for this table and make it primary key.
In case of composite primary key, it should have atleast one not null value(For each row) in the combination of columns. And the combination of column must be unique at all case.
For further details check, http://docs.oracle.com/cd/B10500_01/server.920/a96524/c22integ.htm
Correction - If composite primary key is made up of 3 columns, then no column (among 3) can hold NULL value. And the combination of those 3 columns must be unique.
E.g. (1,2,2)
(1,2,1)
(2,2,1)
(1,2,2) - not valid
Table 1:
Name, x1-X2, fk1, fk2.
Table 2:
K1(parent for table 1),X
How to update table 1 whose second column x1-x2 depands on fk1,fk2 from Table 2
Table1:
a,1.0,1,2
b,-3.0,2,3
Table 2
1,4.0
2,5.0
3,2.0
With this setup:
CREATE TABLE table2 (k NUMBER PRIMARY KEY, x NUMBER);
CREATE TABLE table1 (
NAME VARCHAR2(10) PRIMARY KEY,
diff NUMBER,
fk1 NUMBER REFERENCES table2,
fk2 NUMBER REFERENCES table2);
the following update will "refresh" the colum table1.diff with the values of table2:
SQL> UPDATE (SELECT child.diff old_diff, parent2.x - parent1.x new_diff
2 FROM table1 child
3 JOIN table2 parent1 ON (child.fk1 = parent1.k)
4 JOIN table2 parent2 ON (child.fk2 = parent2.k))
5 SET old_diff = new_diff
6 WHERE old_diff != new_diff
7 OR (old_diff IS NULL AND new_diff IS NOT NULL)
8 OR (old_diff IS NOT NULL AND new_diff IS NULL);
Only the rows that need updating will be refreshed (thanks to the where clause).
Not quite sure I understand the question, referential integrity constraints do not prevent you from updating a table. If you need to do a lot of work in a transaction you can look into Deferred Constraints. Is there any chance you could clarify what you mean?
Not sure exactly what the problem is, maybe you need to rephrase the question a little.
In general, the foreign key constraint makes sure that there exists a corresponding row in the referenced table.
When you update a row with a foreign key, and try to set a value that does not point to such a master row, you will get an error, either immediately or when you commit (depending on when the constraint is enforced, it can be deferred).
Other than that, the update is no different than any other update.
Since the data in table 1 is dependent on the data in table 2 you won't be able to "Update" table 1 directly.
You will have to perform the update on table 2 and then recalculate table 1.
You could do it inside a transaction or perhaps a trigger on table 2.
Another option may be to have table one only hold the foreign keys and the name and then create a view that calculates the X1-X2 value.
EDIT
After looking at the sample data, I don't think you can unambiguously have table 2 be updates as a result of an update on table 1.
For example if you update the second column of table 1 to be 43, how would you know what values to set the specific rows of table 2 (it could be 40 and 3, 20 and 23, etc.)