How to find all pizzerias that serve every pizza eaten by people over 30?

Question

I\'m following the Stanford Database course and there\'s a question where we have Find all pizzerias that serve every pizza eaten by people over 30 using Re

Answer 1

Here is the conversion of http://oracletoday.blogspot.com/2008/04/relational-algebra-division-in-sql.html to MySQL

    mysql>create table parts (pid integer);
    mysql>create table catalog (sid integer,pid integer);
    mysql>insert into parts values ( 1), (2), (3), (4), (5);
    mysql>insert into catalog values (10,1);

mysql>select * from catalog;
+------+------+
| sid  | pid  |
+------+------+
|   10 |    1 |
|    1 |    1 |
|    1 |    2 |
|    1 |    3 |
|    1 |    4 |
|    1 |    5 |
+------+------+


mysql> select distict sid,pid from (select sid from catalog) a  join parts;
+------+------+
| sid  | pid  |
+------+------+
|   10 |    1 |
|   10 |    2 |
|   10 |    3 |
|   10 |    4 |
|   10 |    5 |
|    1 |    1 |
|    1 |    2 |
|    1 |    3 |
|    1 |    4 |
|    1 |    5 |
+------+------+


mysql>select * from 
(select distinct sid,pid from (select sid from catalog) a ,parts)  b where
not exists (select 1 from catalog c where b.sid = c.sid and b.pid = c.pid);

+------+------+
| sid  | pid  |
+------+------+
|   10 |    2 |
|   10 |    3 |
|   10 |    4 |
|   10 |    5 |
+------+------+


mysql>select distinct sid from catalog c1
where not exists (
   select null from parts p
   where not exists (select null from catalog where pid=p.pid and c1.sid=sid));
+------+
| sid  |
+------+
|    1 |
+------+