A foreign key is a field (or collection of fields) in one table that uniquely identifies a row of another table or the same table. In simpler words, the foreign key is defined in a second table, but it refers to the primary key in the first table.
I'm using SQL Developer but I can't seem to find which column in my table holds the foreign key to the other table. When I click on the table, a bunch of tabs show up, among which is the Constraints tab. Here, I can see the foreign key, but I don't see which columns are involved in it.
Open Constraints tab. When you click one of the foreign key constraint name, columns wihch is used in the foreign key references will be seen in the Columns view at the bottom of Constraints Tab
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Hi all,
Can any understand what's going on here?
The case is:
There are 2 tables, called "matricula" and "pagament" with a 1:1 relationship cardinality.
Table matricula primary key composed by 3 fields "edicio","curs" and "estudiant".
Table pagament primary key, the same as above. Furthermore, it references matricula.
As shown, trying to insert a row in pagament table is rejected because it does not exists a row in table matricula. However, asking for this row returns one result.
What am I missing?
Thanks you all
Carles
The problem is that the order of the fields in both tables is not the same, and, moreover, the restriction of the foreign key in table pagament, said that
foreign key (estudiant,curs,edicio) references matricula
without specifying the matricula fields.
It's been solved by setting this restriction as
foreign key (estudiant,curs,edicio) references matricula(estudiant,curs,edicio)
I have a requirement of deleting records from the Postgres database tables.
We have a Customer table which is the main table, this table contains a primary key which is used in so many other tables as a FOREIGN KEY, I want to delete one of the customers as well as its reference used in other tables. Is there any way to delete the customer from main table as well as from other tables which contains foreign key.
Thanks in Advance.
In the other tables, you want a cascading delete foreign key reference. You can create one in the database using:
alter table othertable add constraint fk_othertable_customerid
foreign key (customerid) references customers(customerid)
on delete cascade;
Note: This assumes that customerid is the name of the column in both tables and that it is already defined in the other tables.
A cascading foreign key constraint does exactly what you specify. When a row is deleted in the reference table, then all related rows are deleted.
If you already have foreign key constraints on customerid, then drop the existing constraint and add the cascading version.
Normally when creating constraint between two tables i used to use following script:
ALTER TABLE userVendor
ADD CONSTRAINT myrelation
FOREIGN KEY (DataSource, userId)
REFERENCES user(DataSource, userId)
so userVendor table references user table
Now let's say userVendor becomes association table between two tables. Therefore we have additionally third table called Vendor which has datasource and vendor id as composite key. All of them by the way having composite keys.
How to modify my script to say like (wrong script so far):
ALTER TABLE userVendor
ADD CONSTRAINT myrelation
FOREIGN KEY (DataSource, userId, vendorid)
REFERENCES user(DataSource, userId)
REFERENCES user(DataSource, vendorid)
You'll have to add two foreign key constraints, each referencing one table. It is no problem if a column appears in both constraints.
You will need two ADD CONSTRAINT clauses in your ALTER TABLE statement.
i am new to oracle 10g. I am using it to build some forms. I have created all the tables in sql+ and i have designed my forms. I am having a problem with the foreign key fields in the form.
I have a table named class, class has 4 foreign keys which are represented on the class form
R_ID which is the primary key of a table called ROOM
E_ID which the primary key of a table called EXAM
T_ID which is the primary key of a table called TERM
SUB_ID which is the primary key of a table called SUBJECT
In the class form i want the user to be able to create or update a record of a class. For user friendliness i want when they put the cursor on any one of the foreign key field to enter its value, I want the corresponding NAME from the parent table to be displayed as a drop down list instead/as well as the numerical foreign key value. The user's choice would populate the foreign key field of the class table so
IF R_ID = RM001 and the name of that room in the parent table is Chemistry LAB. I want the user to see chemistry lab and choose that but it populates the class table in the database as RM001
I have created all my navigation manually via buttons, this is the last thing i have to do and im stumped. I want the user to be able to click the field and the drop down list automatically appears.
Any ideas? thanks very much
Found the answer for people you are seeking this information
Use the list of values (lov) wizard.
Build query in the wizard by selecting the attributes of the table you want( the parent table of the foreign key)
Set the return value as the foreign key in the child table
Assign a button to execute the lov created
This works
I'm using inheritance and I ended up having a problem.
If I run:
select count(*) from estate_properties where id = 86820;
I get 1.
But when I try to run this:
insert into property_images (binary_image, name, property_id) values (16779, 'IMG_0096.jpg', 86820)
I get:
********** Error **********
ERROR: insert or update on table "property_images" violates foreign
key constraint "property_images_property_id_fkey" SQL state: 23503
Detail: Key (property_id)=(86820) is not present in table
"estate_properties".
Also ID on estate_properties is SERIAL.
Note: Another table apartments inherits from estate_properties, and 86820 was added to it. Would that make a difference? Also why would it I still have the ID in the parent table and I can select if from there.
Edit:
Looking more closely at the documentation:
http://www.postgresql.org/docs/9.5/static/ddl-inherit.html
I want to achieve this:
5.9.1. Caveats
Specifying that another table's column REFERENCES cities(name) would
allow the other table to contain city names, but not capital names.
There is no good workaround for this case.
EDIT2:
Here is the declaration of the foreign key:
CONSTRAINT property_images_property_id_fkey FOREIGN KEY (property_id)
REFERENCES estate_properties (id) MATCH SIMPLE
ON UPDATE NO ACTION ON DELETE NO ACTION
Apparently the answer is here:
Foreign keys + table inheritance in PostgreSQL?
A foreign key can point to a table that is part of an inheritance hierarchy, but it'll only find rows in that table exactly. Not in any parent or child tables. To see which rows the foreign key sees, do a SELECT * FROM ONLY thetable. The ONLY keyword means "ignoring inheritance" and that's what the foreign key lookup will do