sql語句優化日記1

EXPLAIN 
SELECT
(
SELECT COUNT(*)
FROM emp
WHERE depid =(SELECT depid
FROM dep
where dname='lnHwlS' ))
+
(
SELECT COUNT(*)
FROM emp
WHERE depid =(SELECT depid
FROM dep
where dname='thJHsQ'))


EXPLAIN 
SELECT count(*)
FROM emp
WHERE depid in (SELECT depid
FROM dep

where  dname='thJHsQ' or dname='lnHwlS' )