Queries

[mmcclaf]

This came in the Python groups, and I put one up in the database
group, since I will later have to use Python to access the SQL file,
so therefore tackling one thing at a time. Also, there were no answers
that were coming up in the .database group.

On top of that:
>        Really? You can have ships in the Outcomes relation that DO NOT
>APPEAR in the Ships relation... Goodbye referential integrity.
>
>        Besides which, if they don't appear in the Ships relation, then
>there is NO INFORMATION to tell you what ship CLASS it is a member of --
>do you group them all as "UNKNOWN" class, or do you declare each to be
>the only ship of its class (and thereby use the ship name as the class
>name)?

This meant that some ships weren't listed in the Ship table provided
but did show up in the Outcome. Therefore, they are not directly
referenced one to the other.

>        <sigh> Another gmail user found only by back referencing responses...

What is meant by this statement?

So in short of the responses given, I need to study further: GROUP BY,
HAVING, AS, COUNT, and subselect queries, right?

The relational algebra, I am able to translate it into SQL, or most of
it, meaning turning it into the queries of SQL. This is not an
advanced database course, but more a basic intro to database systems.