Return every compound lighter than 50 g/mol, with its name, its formula and its mass, lightest first. A document carries the weight on the compound itself and calls it mass, where the tables keep it in structures.molecular_weight — the two shapes place and name the same number differently. Nine compounds answer this. Water and ammonia are among them.
A beginner exercise, answered in Mango. It is marked by the rows your query returns rather than by how you wrote it, with 3 hints if you want them.
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.