Sql Count（*）单个查询中每个id的相关项数[duplicate]

I honestly don't know what exactly to put in the title, but here goes the problem:

I have table(movie_actor) referring to actors and movies they are related with. Something like:

AID | MID
AC01 | MV1
AC02 | MV1
AC01 | MV2
AC02 | MV3
AC01 | MV3

So I have come up on how to get for example all movies relating to MV1 through its actors through this sql query:

SELECT movie_actor.MID
FROM movie_actor
WHERE AID
IN ( SELECT AID FROM movie_actor WHERE IN MID = "MV1") AND movie_actor.MID<>"MV1"

that would result to:

MID: MV2, MV3

Now what I really want to get is this related movies to MV1 and their corresponding number of related movies. Basically:

MID | Number of Related Movies
MV2 | 2 (MV1, MV3)
MV3 | 2 (MV1, MV2)

Now I can get this using count(*) and the query I mentioned earlier.

SELECT COUNT(*)
FROM movie_actor
WHERE AID
IN (
SELECT AID
FROM movie_actor
WHERE MID="MV2")

But I have to do so individually which I can do away with php(tried it,slow with large amount of data). Is it possible to do it in one query?

also if i am able to do this, will it be faster as oppose to doing it in php?

sorry if I have weird formatting, new here :) also pardon the noobness

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SELECT movie_actor.MID FROM movie_actor WHERE AID IN ( SELECT AID FROM movie_actor WHERE IN MID = "MV1") group by MID