In our database we happen to have a foreign key constraint that has an empty from column
It looks something like this
fk_1049376c154c25f8 FOREIGN KEY () REFERENCES table2 (id)
What does this denote and where is a documentation in the Postgres documentation for this
I see three possible meanings
use the same column name as referenced in the second table so meaning (id) references table2 (id) implicitly
use the primary key which would be id in this table so it might also be (id) references table (id)
or monitor all columns (*) references table2 (id) which actually seems to be the way this behaves but does not make any sense to me in using it
Can anyone point me to a correct explanation or some read that confirms any of my theories or gives me the real truth?
Trying to use this throws a syntax error in PostgreSQL 9.3 at least.
postgres=# alter table test add foreign key () references test(id);
ERROR: syntax error at or near ")"
LINE 1: alter table test add foreign key() references test(id);
I am guessing this comes from psql \d or something so it sounds like something wrong in your database, perhaps some sort of catalog corruption.
At any rate it is not a valid syntax and you should look into where this is coming from and fixing it.
Related
I have a PostgreSQL table containing a bunch of foreign keys pointing to another table:
create table foo (
hourly00 uuid references hourly(id),
hourly01 uuid references hourly(id),
-- etc.
hourly23 uuid references hourly(id),
-- omit rest
);
Admittedly, this looks silly (and I am lucky to have only 24 of such keys), but I have not found anything better.
In the meantime, I stumbled on PostgreSQL documentation about arrays (I did not know about PostgreSQL arrays before). I got an idea and I tried this:
create table foo (
hourly uuid[24] references hourly(id)
);
which, of course, immediately resulted in an error:
ERROR: foreign key constraint "main_hourly_fkey" cannot be implemented
DETAIL: Key columns "hourly" and "id" are of incompatible types: uuid[] and uuid.
But then I got another idea — to ask about my situation on StackOverflow. So my question is: does PostgreSQL provide means for doing something like this, i.e. for having an array of foreign keys in a table? Is it perhaps doable with some PL/*? Or perhaps with some other database system? I am willing to do my own research, but I have no idea as to where to look.
I have an ALTER TABLE statement, written in T-SQL (SQL Server):
ALTER TABLE myTable WITH CHECK ADD CONSTRAINT [FK_myTable_myColumn] FOREIGN KEY(myColumn) REFERENCES otherTable (Column)
If I want to translate this statement in Postgresql, how can I make this? Paying attention to WITH CHECK ADD CONSTRAINT
You need to
remove WITH CHECK - I don't know what this is supposed to do, but you can't have a "check constraint" together with a foreign key constraint in Postgres
use standard compliant identifiers (without the square brackets)
ALTER TABLE my_table
ADD CONSTRAINT fk_mytable_mycolumn
FOREIGN KEY(my_column) REFERENCES other_table (column)
I'm trying to truncate a set of tables, but it keeps complaining about a foreign key.
but that foreign key is set to on delete Set null
to reproduce:
create table test_players (id SERIAL PRIMARY KEY, name VARCHAR(255));
create table test_items (id SERIAL PRIMARY KEY, name VARCHAR(255), player_id INTEGER FOREIGN KEY (player_id) REFERENCES test_players(id) ON DELETE SET NULL);
now if you truncate the test_players it will complain:
ERROR: cannot truncate a table referenced in a foreign key constraint
DETAIL: Table "test_items" references "test_players".
HINT: Truncate table "test_items" at the same time, or use TRUNCATE ... CASCADE.
SQL state: 0A000
what must I do to make me be able to delete test_players without deleting the test_items?
You cannot do what you are attempting. You will have to do this in 3 steps.
Update test_items and for each player_id. Well technically you don't need this, but if you don't give yourself data integrity issues.
Drop the test_items to test_players FK.
Then truncate test_players
The reason is that truncate basically just zaps the table, it does NOT process individual rows. Therefore it would not process the FK set null, it throws the error you got instead. In fact even if the child table is empty, or for that matter even if the parent is empty. See fiddle here. The fiddle also contains a function to do it, and a test for it.
The of course you could just Delete from test_players and let the triggers take care of updating test_items. Takes longer, esp if larger table, but you keep your FK. Of course there's
Recreate your FK.
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
I'm using postgresql 9.1 on Ubuntu 12.04. I have a user defined type as one column of a table. When I create a primary key constraint I get a syntax error.
Here is a sample sql script I'm using with psql to create the table:
CREATE TYPE my_type AS
(
field1 integer,
field2 integer
);
CREATE TABLE my_table
(
my_data my_type,
other_data integer
);
ALTER TABLE my_table ADD CONSTRAINT pk_my_table PRIMARY KEY (my_data.field1);
I get this error:
ERROR: syntax error at or near "."
LINE 1: ...ble ADD CONSTRAINT pk_my_table PRIMARY KEY (my_data.field1);
I've tried using (my_data).field1 but also get a syntax error.
If I just use my_data in the constraint there is no error:
ALTER TABLE my_table ADD CONSTRAINT pk_my_table PRIMARY KEY (my_data);
But I would like to use just one field as part of the constraint.
Thanks for any ideas.
I found this question using google and I'm pretty sure is dead but I still want to answer it cause someone else might see it.
Short answer is you have to use the field's name:
ALTER TABLE "public"."carga" ADD CONSTRAINT "pk_my_table" PRIMARY KEY ("field1");