Why one of my query won't serve from cache

I’m tring to save a query result to Memcache, but, as shown in the log below, though it was saved to the cache, but it still did the query.

By the way. There is a function like this one executed ahead of it and the result was successfully served from cache, but this one didn’t work.


Update[/b]:Thank everyone.I think I’ve found the reason:The query result is null, so it will always do the query but not save it into cache