Sql Column Name In Quotes

The presence of a column named id in every table is so common that this has become synonymous with a primary key. Programmers learning SQL get the false idea that a primary key always means a column defined in this manner.

In a RDBMS, since all the column names and types are defined at the table level, this information does not need to be replicated in each row. MongoDB, by contrast, doesn’t know, at the collection level, what fields are present in each document, nor does it know their types, so this information must be stored on a per-document basis.