SQL query to select only grandchildren

Question

I\'m pretty new to SQL, trying to wrap my head around it, but it\'s getting a little confusing. Here\'s a simplified version of what I\'m working with.

I have this

Answer 1

This is without JOIN statement, but as a SQL learner, I find it as easier:

1. For grandchildren:

   SELECT grandparent.name AS Grandparents, grandchild.name AS Grandchildren 
   FROM people AS grandparent, people AS parent, people
   AS grandchild WHERE grandchild.parent_id = parent.id 
   AND parent.parent_id = grandparent.id;
   

2. For children:

   SELECT parent.name as Parent, child.name AS Child 
   FROM people AS parent, people AS child 
   WHERE child.parent_id = parent.id AND parent.parent_id = 0;
   

3. And for all children-parent pairs:

   SELECT parent.name as Parent, child.name AS Child 
   FROM people AS parent, people AS child 
   WHERE child.parent_id = parent.id;
   

It took me a while, but it was fun :D