Provide a way to do data preview

[whitewum]

Is your feature request related to a problem? Please describe.

When you have a Database with new data, the first SQL command will be

select * from tables limit 10;

to do a data preview. So as the Cypher command

Match (n)
Return n
Limit 10

But, there is no corresponding command in nGQL. And I've been asked about this question so many times.

Describe the solution you'd like

Match (n)
Return n
Limit 10

is OK to me. A new command clause is also accepted but not recommended.

Describe alternatives you've considered
the count(*) command

select count(*) from tables;

or

Match (n)
Return count(n)

is also frequently used. So I hope there is a counterpart in nGQL.

Additional context
I know the storage can provide a scan api, so I think select *, select count(*) can be implemented in Nebula.