Step 7 of 18 of the SQL tutorial. There is no boiling point column on compounds, and that is deliberate: a boiling point is one supplier's claim, measured at one pressure, so it hangs off catalog_entries through a foreign key. Ask 1,2-Diaminocyclohexane for its boiling point and three answers come back — 188 °C at 760 mmHg, 104 °C at 40 mmHg, 79 °C at 15 mmHg. That is vacuum distillation, and normalisation is what keeps all three. Mango needs no join here, because the document already nests the listings under the compound.
It opens on the query SELECT c.preferred_name, e.entry_id, e.supplier, b.low_c, b.high_c, b.pressure_mmhg FROM compounds c JOIN catalog_entries e ON e.compound_id = c.id JOIN boiling_points b ON b.catalog_entry_id = e.id WHERE c.preferred_name = '1,2-Diaminocyclohexane' ORDER BY b.pressure_mmhg DESC, which you can run and change in place.
Ask the same question of a chemical dataset in SQL and in Mango and compare the two answers. The database is a SQLite file your browser downloads once and queries locally, so nothing you write ever leaves your machine — which is also why the tool needs JavaScript.