Factor/To do/DB

• omitting certain columns from result tuples
• foreign keys
• compound primary keys

i want these operations to be performed with a constant number of queries:

1. get the most recent 20 posts, by date. Get the number of comments in each post.
2. get the number of posts per month, in the last 12 months.
3. delete all posts with uid=$1, delete all comments whose parent post has uid=$1, delete all comments with uid=$1
4. delete all annotations with parent paste=$1, delete paste with id=$1.