MySQL Go heavy

Select A.id,a.ssmz, (select count (SSMZ) from Shop_tourist_key b where b.ssmz=a.ssmz) as Count
From Shop_tourist_key a WHERE a.ssmz are not null GROUP by A.SSMZ LIMIT 0, 3;

Select A.id,a.ssmz, (select count (SSMZ) from Shop_tourist_key b where b.ssmz=a.ssmz) as Count
From Shop_tourist_key a where ISNULL (A.SSMZ) =false GROUP by A.ssmz ORDER by Count DESC
LIMIT 0, 3;

Select A.id,a.ssmz, (select count (SSMZ) from Shop_tourist_key b where b.ssmz=a.ssmz) as Count,
COUNT (distinct A.SSMZ) from Shop_tourist_key a group by a.ssmz LIMIT 0,3;

MySQL Go heavy