How to use Maps and map functions

[rfraposa]

We should add a KB article

[ParthNarkhede]

Hey! I want to write an article on How to use maps and map function as mentioned and contribute for the same...

[rfraposa]

That would be awesome - thanks! Add a new markdown file here (https://github.com/ClickHouse/clickhouse-docs/tree/main/knowledgebase) and create a PR. I'll be happy to review it.