sql（join带代替in）

EXPLAIN 
SELECT count(*)
FROM emp
WHERE depid not IN( SELECT depid
FROM dep

WHERE dname ='bLByMr' or dname = 'pyuDKO')

EXPLAIN 
SELECT count(*)
FROM emp join dep on emp.depid=dep.depid
WHERE dname !='bLByMr' and dname != 'pyuDKO'

EXPLAIN 
SELECT count(*)
FROM emp
WHERE depid  IN( SELECT depid
FROM dep
WHERE dname ='bLByMr' or dname = 'pyuDKO')

EXPLAIN 
SELECT count(*)
FROM emp join dep on emp.depid=dep.depid
WHERE dname ='bLByMr' or dname = 'pyuDKO'