Can set the value of the previous query

Question

how to SET return value to new query ?

query like :

DECLARE @count;   

SELECT COUNT(*) FROM a WHERE x = 1;

SET @count = //result_last_query

SELECT * FROM b WHERE z = @count;

Answer 1

As simple as :

 SELECT *  FROM b
     where z=(select count(*) FROM a FROM a WHERE x = 1;)}

You dont even require any variable declaration

Answer 2

thanks good solution

I modified the code of answers

SELECT  *
FROM    B
WHERE   id IN (
                SELECT COUNT(*) AS count
                FROM A
                WHERE x = 1
              )