Collections of Documents on the other hand, offer a much more relaxed approach. Collections are just namespaces where we insert documents. Documents are objects of any schema and format; but in practice, it almost always is JSON. There are no enforced types, no constraints, no guarded references between documents in different collections. In the same collection, we might have documents of completely different schema - flexibility and openness to any data and column types rules here. In tables, rows have columns of simple, scalar types (mostly) - numbers, ids, strings, dates, timestamps and so on. In collections, documents have fields comprising both simple and composite types like arrays and other documents, nested inside. Same field in different documents, but still of the same collection, might have different types as well - almost anything is allowed here.
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