On 10/14/17 5:35 AM, Simon Slavin wrote:
On 14 Oct 2017, at 10:30am, Csányi Pál <csanyi...@gmail.com> wrote:
With which constraints can one create a foreign key to
first: get one to one relationship, and
second: one to many relationship?
Foreign keys always implement a one-to-many relationship.
You could enforce a one-to-one relationship by using one foreign key in each
direction. But there could be problems when getting the data in in the first
place — which one do you put in first ?
<https://sqlite.org/foreignkeys.html>
If you have problems with the above page, please post again.
Simon.
One way to make them build one to at-most-one relationships is too add a
unique index on the foreign key, then it can only occur once.
A True one-one relationship by the normailization rules says that they
should all be in the same record.
--
Richard Damon
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