您需要在查询中应用联接，因此，数组将被视为规范化实体，然后可以应用过滤器.

You need to apply a join on your query, so then you array will be treated as a normalized entity and then you can apply the filter.

select c.id, a.message
from c join a in c.activities
where CONTAINS(a.message,"activity")

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