Am 21. Juli 2019 02:58:05 MESZ schrieb Karen Goh <karenworld@xxxxxxxxx>: >Hi all, > >With PG4Admin, I am lost. Since pgadmin4 is just a frontend, you're not "lost with pgadmin4", but maybe with postgresql. >I realised now that the keys are not created and perhaps that is why >the join query is not working out. Creating a foreign key doesn't magically create the necessary keys for it. >Please let me know what is the correct way to alter a column in a table >to have foreign key to a tutor_id which is also the primary key of that >table. > >So, meaning I need to create a foreign key as well as primary key for >tutor_id. > >So far, this is what I have attempted but it is not working. >ALTER TABLE tutor_subject > ADD CONSTRAINT tutor_subject_pk > PRIMARY KEY (tutor_id) > ADD CONSTRAINT tutor_subject_fk > FOREIGN KEY (tutor_id) This looks like a 1:1 relationship which is to be avoided. One ALTER TABLE command either adds a primary or a foreign key. There is no FK without the keyword REFERENCES. FK relationships help in keeping the data consistent, but they are totally unrelated to/useless for SELECT statements and their JOIN operations. This is a common misconception. Regards, Holger -- Holger Jakobs, Bergisch Gladbach +49 178 9759012 - sent from mobile, therefore short -
