FK issue

mike <mike@bristolreccc.co.uk> writes:

I have set up a FK as follows

ALTER TABLE lk_sub_con ADD FOREIGN KEY (type) REFERENCES
lk_sort_of_contact(type_code);

However when I do this

INSERT INTO lk_sort_of_contact (type_code) VALUES ('1') (ie: a NULL into
the FK) it works

Is this a bug?

No.

NULLs are permitted in referencing columns unless that column is
declared NOT NULL.

-Doug

mike <mike@bristolreccc.co.uk> writes:

INSERT INTO lk_sort_of_contact (type_code) VALUES ('1') (ie: a NULL into
the FK) it works

Is this a bug?

No. Mark the column NOT NULL if you wish to disallow nulls.

regards, tom lane

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On Thursday 10 June 2004 08:21 am, mike wrote:

I have set up a FK as follows

ALTER TABLE lk_sub_con ADD FOREIGN KEY (type) REFERENCES
lk_sort_of_contact(type_code);

However when I do this

INSERT INTO lk_sort_of_contact (type_code) VALUES ('1') (ie: a NULL into
the FK) it works

Is this a bug?

No.
you have a table lk_sub_con. That table has the foreign key assigned.
This means it doesn't matter what you put into lk_sort_of_contact , it matters
what you put into lk_sub_con.
The foreign key says something like
"If you put a value into field type of table lk_sub_con, the same value must
be existant in table lk_sort_of_contact field type_code"

Try to add a null value to lk_sub_con.type - or any value that's not in
lk_sort_of_contact. Postgres will throw an error.
If you don't want nulls in the referenced table lk_sort_of_contact you have to
define that there. Maybe you make the field type_code unique or the primary
key.

UC

- --
Open Source Solutions 4U, LLC 2570 Fleetwood Drive
Phone: +1 650 872 2425 San Bruno, CA 94066
Cell: +1 650 302 2405 United States
Fax: +1 650 872 2417
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On Thu, 2004-06-10 at 17:03, Uwe C. Schroeder wrote:

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On Thursday 10 June 2004 08:21 am, mike wrote:

I have set up a FK as follows

ALTER TABLE lk_sub_con ADD FOREIGN KEY (type) REFERENCES
lk_sort_of_contact(type_code);

However when I do this

INSERT INTO lk_sort_of_contact (type_code) VALUES ('1') (ie: a NULL into
the FK) it works

this should have said

INSERT INTO lk_sub_con (sub_cat) VALUES ('1') (ie: a NULL into
the FK) it works ie: a NULL in type

(wrong copy)

Is this a bug?

No.
you have a table lk_sub_con. That table has the foreign key assigned.
This means it doesn't matter what you put into lk_sort_of_contact , it matters
what you put into lk_sub_con.
The foreign key says something like
"If you put a value into field type of table lk_sub_con, the same value must
be existant in table lk_sort_of_contact field type_code"

Try to add a null value to lk_sub_con.type - or any value that's not in
lk_sort_of_contact. Postgres will throw an error.

this is the problem - it doesnt if I put a null in (the refernced column
has no nulls)

If you don't want nulls in the referenced table lk_sort_of_contact you have to
define that there. Maybe you make the field type_code unique or the primary
key.

It is

UC

For info

SELECT type_code FROM lk_sort_of_contact; type_code
----------- 3 6 5 1
2
4
7
9
8
10
11
12
13
14
16
17
20
21

SELECT * FROM lk_sub_con;
sub_id | type | sub_cat | scat_desc
--------+------+---------+-----------
1 | | 1 |
2 | | 20 |
3 | 21 | 22 |

(after the above FK & INSERT)

- --

On Thu, 10 Jun 2004, mike wrote:

On Thu, 2004-06-10 at 17:03, Uwe C. Schroeder wrote:

Try to add a null value to lk_sub_con.type - or any value that's not in
lk_sort_of_contact. Postgres will throw an error.

this is the problem - it doesnt if I put a null in (the refernced column
has no nulls)

NULLs in a referencing column are a special case in the spec. For a
single column key, a NULL is considered to pass the constraint. For
multiple column keys it depends on the match type.

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On Thursday 10 June 2004 09:27 am, mike wrote:

On Thu, 2004-06-10 at 17:03, Uwe C. Schroeder wrote:

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On Thursday 10 June 2004 08:21 am, mike wrote:

I have set up a FK as follows

ALTER TABLE lk_sub_con ADD FOREIGN KEY (type) REFERENCES
lk_sort_of_contact(type_code);

However when I do this

INSERT INTO lk_sort_of_contact (type_code) VALUES ('1') (ie: a NULL
into the FK) it works

this should have said

INSERT INTO lk_sub_con (sub_cat) VALUES ('1') (ie: a NULL into
the FK) it works ie: a NULL in type

(wrong copy)

Is this a bug?

No.
you have a table lk_sub_con. That table has the foreign key assigned.
This means it doesn't matter what you put into lk_sort_of_contact , it
matters what you put into lk_sub_con.
The foreign key says something like
"If you put a value into field type of table lk_sub_con, the same value
must be existant in table lk_sort_of_contact field type_code"

Try to add a null value to lk_sub_con.type - or any value that's not in
lk_sort_of_contact. Postgres will throw an error.

this is the problem - it doesnt if I put a null in (the refernced column
has no nulls)

NULL is simply no value. A foreign key only checks for values.
Modify lk_sub_con to have a "NOT NULL" in the definition of type.
NOT NULL forces the field type to have a value and whenever there's a value
the foreign key will kick in.

UC

- --
Open Source Solutions 4U, LLC 2570 Fleetwood Drive
Phone: +1 650 872 2425 San Bruno, CA 94066
Cell: +1 650 302 2405 United States
Fax: +1 650 872 2417
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