In what locations can a subquery be used?

In the following code I mark locations within a query where to my understanding a subquery 开发者_开发问答can be used:

from   c1 in subquery
from   c2 in subquery
where  c2 = subquery
let    c3 = subquery
select new{ result = subquery };

Are there any other locations where a subquery can be used?

Thank you

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where subquery.Contains(value)