{"action":"created","issue":{"url":"https://api.github.com/repos/datajoint/datajoint-python/issues/113","labels_url":"https://api.github.com/repos/datajoint/datajoint-python/issues/113/labels{/name}","comments_url":"https://api.github.com/repos/datajoint/datajoint-python/issues/113/comments","events_url":"https://api.github.com/repos/datajoint/datajoint-python/issues/113/events","html_url":"https://github.com/datajoint/datajoint-python/issues/113","id":92043052,"number":113,"title":"Relations whose primary keys have zero attributes","user":{"login":"dimitri-yatsenko","id":1096169,"avatar_url":"https://avatars.githubusercontent.com/u/1096169?v=3","gravatar_id":"","url":"https://api.github.com/users/dimitri-yatsenko","html_url":"https://github.com/dimitri-yatsenko","followers_url":"https://api.github.com/users/dimitri-yatsenko/followers","following_url":"https://api.github.com/users/dimitri-yatsenko/following{/other_user}","gists_url":"https://api.github.com/users/dimitri-yatsenko/gists{/gist_id}","starred_url":"https://api.github.com/users/dimitri-yatsenko/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/dimitri-yatsenko/subscriptions","organizations_url":"https://api.github.com/users/dimitri-yatsenko/orgs","repos_url":"https://api.github.com/users/dimitri-yatsenko/repos","events_url":"https://api.github.com/users/dimitri-yatsenko/events{/privacy}","received_events_url":"https://api.github.com/users/dimitri-yatsenko/received_events","type":"User","site_admin":false},"labels":[],"state":"open","locked":false,"assignee":null,"milestone":null,"comments":1,"created_at":"2015-06-30T09:40:13Z","updated_at":"2015-06-30T09:47:54Z","closed_at":null,"body":"Currently datajoint prohibits creating tables with no attributes in the primary key.  We can relax this prohibition. \r\n\r\nIf the primary key has no attributes, it can only have one value.  Therefore, the relation can only contain one tuple.  So it's good for relations that contain a single fact about the universe rather than a collection of similar facts.  The relational algebra using such relations remains identical to what it is now.  In particular, joining two relations with no primary key produces another relation with no primary key and one tuple."},"comment":{"url":"https://api.github.com/repos/datajoint/datajoint-python/issues/comments/117099771","html_url":"https://github.com/datajoint/datajoint-python/issues/113#issuecomment-117099771","issue_url":"https://api.github.com/repos/datajoint/datajoint-python/issues/113","id":117099771,"user":{"login":"dimitri-yatsenko","id":1096169,"avatar_url":"https://avatars.githubusercontent.com/u/1096169?v=3","gravatar_id":"","url":"https://api.github.com/users/dimitri-yatsenko","html_url":"https://github.com/dimitri-yatsenko","followers_url":"https://api.github.com/users/dimitri-yatsenko/followers","following_url":"https://api.github.com/users/dimitri-yatsenko/following{/other_user}","gists_url":"https://api.github.com/users/dimitri-yatsenko/gists{/gist_id}","starred_url":"https://api.github.com/users/dimitri-yatsenko/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/dimitri-yatsenko/subscriptions","organizations_url":"https://api.github.com/users/dimitri-yatsenko/orgs","repos_url":"https://api.github.com/users/dimitri-yatsenko/repos","events_url":"https://api.github.com/users/dimitri-yatsenko/events{/privacy}","received_events_url":"https://api.github.com/users/dimitri-yatsenko/received_events","type":"User","site_admin":false},"created_at":"2015-06-30T09:47:54Z","updated_at":"2015-06-30T09:47:54Z","body":"Note that this is different from SQL's tables that don't have a primary key.  SQL is not exactly relational and its tables can contain duplicate rows.  SQL does not have the equivalent of a primary key with zero attributes as defined here."}}