Using relational database tables in SQL

SQL: Tables can be joined with other tables to compute useful information. For example:

How many structures are matched by each atom/fragment type?

Update xlogp.simplex set train_freq = (select count(smiles) from xlogp.training_set
where matches(smiles,smarts) group by smarts);

Which structures contain atoms not matched by any atom type?

Select smiles from training_set, atom_types group by smiles
having count_matches(smiles,'*') <> sum(count_matches(smiles,smarts));

• No smiles found, as expected

Which atom types are in my new training set that were not in the original training set?

Select smarts from epa.hanschleo1985_atom_types
   Except
Select smarts from xlogp.atom_types;