with the prior experience of mysql or mongoDb or any other. Documentation can be understood. But without any experience of those, hard to try the JSONB data type.
The functions chapter assumes that one has read the earlier "Data Types" chapter for JSON first. There are many examples there.
Specify operand places in a select query (give the entire example query).
That would be unnecessarily verbose in almost all cases. Is there a specific one that is particularly confusing for which a more detailed example should provided?
The function reference chapter assumes that people know how to write queries and just need to know which functions are available. Other chapters in the documentation cover describing how to do the former.
