RELATIONAL QUERY WRITING in ALGEBRA

Write relational algebra queries for all of the following

Consider a database with the following schema.

LIKES(drinker,beer); /* key: all columns */

FREQUENTS(drinker,pub); /* key: all columns */

SERVES(_pub,beer_,cost); /* key: (pub,beer) */

1. Find pubs that serve some beer that Joe likes.

2. Find drinkers who frequent pubs where they can get a drink for less

than $3

3. Find drinkers who like at least one expensive (over $8) beer that Joe likes.

4. Find drinkers who like some beers but do not frequent any pubs.

5. Find drinkers who frequent pubs that serve either Stella Artois or Molsons.

6. Find pubs that serve every beer that Joe likes.

7. Find all drinkers who frequent a pub that serves at least 2 beers they like, and one of them for at most $3.