Left Joins for days

joins.sql

/* create some nodes to connect */
INSERT INTO nodes(title) VALUES
  ('Linux'),
  ('Operating System');

/* create a connection to connect nodes with */
INSERT INTO links(title) VALUES ('is_a');

/* And connect the two nodes created via the link */
INSERT INTO connections(node_a, link, node_b) VALUES
  (1, 1, 2);
  
SELECT
  node_a.title AS node_a,
  node_b.title AS node_b,
  link.title AS link,
  connection.id AS id
FROM connections connection
LEFT JOIN nodes node_a
  ON node_a.id = connection.node_a
LEFT JOIN nodes node_b
  ON node_b.id = connection.node_b
LEFT JOIN links link
  ON link.id = connection.link;