This example uses the exists() function:
MATCH (p:Person)
WHERE exists((p)-[:LIVING_IN]->(:Country {name: 'Germany'}))
RETURN p.name
ORDER BY p.name;
How is that query different than:
MATCH (p:Person)-[:LIVING_IN]->(:Country {name: 'Germany'})
RETURN p.name
ORDER BY p.name
Why should I use the exist() function?
I don't understand what is the difference or use case for the exist() function.
The MATCH clause must look for and remember all matches. But the EXISTS function only needs to find a single pattern match to return TRUE. So EXISTS can speed up a query.
Also, in your first query, no duplicate names will be returned (assuming every person has a different name). But your second query can return duplicate names (since the same person can be found in multiple pattern matches if he has residences in multiple countries).
