Mysql服务器经常性CPU占用100%,按照Mysql解决思路，应该是有大的SQL语句在占用CPU时间。
使用如下命令将语句打印到文本
mysql -uroot -ppasswd -e "show full processlist" > c:\test.txt
使用文本编辑工具分析后
得到如下语句：
select ret.*
from (select tt.sourcetype as sourcetype,
tt.pointtype as pointtype,
tt.upid as upid,
tt.gotdate as gotdate,
tt.credit as credit,
tt.classid as classid,
tt.classname as classname,
tt.xxkc as xxkc,
tt.xskc as xskc,
tt.trainMode as trainMode,
tt.place as place,
tt.courseid as courseid,
tt.coursetype as coursetype,
tt.coursename as coursename,
tt.rewardPointApplyId as rewardPointApplyId,
tt.achieveWay as achieveWay,
tt.type as type
from (select '9' as sourcetype,
uk.C_POINTTYPE as pointtype,
uk.C_OID as upid,
utc.CREATEDATE as gotdate,
uk.credit as credit,
utc.classid as classid,
utc.classname as classname,
utc.xxkc as xxkc,
utc.xianshangkc as xskc,
utc.trainMode as trainMode,
utc.place as place,
'' as courseid,
'' as coursetype,
'' as coursename,
'' as rewardPointApplyId,
'' as achieveWay,
'' as type
from (select distinct (k.C_CLASSID) as C_CLASSID,
'9' as C_POINTTYPE,
'' as C_OID,
k.C_USERID as C_USERID,
sum(k.c_point) as credit
from LES_USERPOINTTASK k
where k.C_USERID = '14964'
and k.C_CLASSID is not null
group by k.C_CLASSID) uk,
(select tc.OID as classid,
tc.CREATEDATE as CREATEDATE,
tc.CLASSNAME as classname,
t1.xxkc as xxkc,
t1.xianshangkc as xianshangkc,
tc.trainMode as trainMode,
tc.place as place
from LMS_CLASS tc
left join (select t0.classid,
group_concat(t0.xianxiakc) as xxkc,
group_concat(t0.xianshangkc) as xianshangkc,
sum(t0.credit) as credit
from (select tcc.CLASS_ID as classid,
CASE
WHEN tcc.THEACH_MODE > 0 THEN
group_concat(tcc.COURSE_NAME)
ELSE
''
END as xianxiakc,
CASE
WHEN tcc.THEACH_MODE > 0 THEN
''
ELSE
group_concat(tcc.COURSE_NAME)
END as xianshangkc,
sum(integration) as credit
from LMS_CLASS_COURSE tcc
group by tcc.CLASS_ID,
tcc.THEACH_MODE) t0
group by t0.classid) t1
on t1.classid = tc.OID) utc
where uk.C_CLASSID = utc.classid
and uk.credit is not null
and uk.C_USERID = '14964'
union
select '9' as sourcetype,
'' as pointtype,
lup.C_OID as upid,
lup.CREATEDATE as gotdate,
lup.C_POINT as credit,
lup.C_CLASSID as classid,
lup.C_CLASSNAME as classname,
'' as xxkc,
'' as xskc,
'1' as trainMode,
ltc.place as place,
'' as courseid,
'' as coursetype,
'' as coursename,
'' as rewardPointApplyId,
'' as achieveWay,
'' as type
from LES_USERPOINTTASK lup, LMS_CLASS ltc
where lup.C_TRAINWAY = '外派'
and ltc.OID = lup.C_CLASSID
and lup.C_USERID = '14964'
union
select cs.C_COURSETYPE as sourcetype,
up.C_POINTTYPE as pointtype,
up.C_OID as upid,
up.CREATEDATE as gotdate,
cs.C_CREDIT as credit,
'' as classid,
'' as classname,
'' as xxkc,
'' as xskc,
'' as trainMode,
'' as place,
cs.C_COURSEID as courseid,
cs.C_COURSETYPE as coursetype,
cs.C_COURSENAME as coursename,
'' as rewardPointApplyId,
'' as achieveWay,
'' as type
from LES_COURSE cs, LES_USERPOINTTASK up
where cs.C_COURSEID = up.C_ONLINECOURSEID
and up.c_classid is null
and up.C_USERID = '14964'
union
select '8' as sourcetype,
'optional' as pointtype,
'' as upid,
rp.C_ACHIEVEDATE as gotdate,
rp.C_REWARDPOINT as credit,
'' as classid,
'' as classname,
'' as xxkc,
'' as xskc,
'' as trainMode,
'' as place,
'' as courseid,
'' as coursetype,
'' as coursename,
rp.C_OID as rewardPointApplyId,
rp.C_ACHIEVEWAY as achieveWay,
rp.C_TYPE as type
from LES_REWARDPOINTAPPLY rp
where rp.C_USERID = '14964'
and rp.C_RESULT = '1'
and rp.C_APPROVESTATUS = '3') tt
where date_format(tt.gotdate, '%Y') = '2017'
order by tt.pointtype) ret limit
针对各段执行结果的评估，查询到该段占用时间最长，需要将近8分钟才能有结果：
select tc.OID as classid,
tc.CREATEDATE as CREATEDATE,
tc.CLASSNAME as classname,
t1.xxkc as xxkc,
t1.xianshangkc as xianshangkc,
tc.trainMode as trainMode,
tc.place as place
from LMS_CLASS tc
left join (select t0.classid,
group_concat(t0.xianxiakc) as xxkc,
group_concat(t0.xianshangkc) as xianshangkc,
sum(t0.credit) as credit
from (select tcc.CLASS_ID as classid,
CASE
WHEN tcc.THEACH_MODE > 0 THEN
group_concat(tcc.COURSE_NAME)
ELSE
''
END as xianxiakc,
CASE
WHEN tcc.THEACH_MODE > 0 THEN
''
ELSE
group_concat(tcc.COURSE_NAME)
END as xianshangkc,
sum(integration) as credit
from LMS_CLASS_COURSE tcc
group by tcc.CLASS_ID,
tcc.THEACH_MODE) t0
group by t0.classid) t1
on t1.classid = tc.OID
其中LMS_CLASS表12800多条记录，LMS_CLASS_COURSE这张表也才9000多条记录，没理由这么慢。在两张表的classid和oid上均存在索引
查看执行计划，并未走索引
改写了SQL结果如下：
SELECT
classid,
CREATEDATE,
classname,
trainMode,
place,
group_concat(t0.xianxiakc) AS xxkc,
group_concat(t0.xianshangkc) AS xianshangkc,
sum(t0.credit) AS credit
FROM
(
SELECT
classid,
CREATEDATE,
classname,
trainMode,
place,
CASE
WHEN tcc.THEACH_MODE > 0 THEN
group_concat(tcc.COURSE_NAME)
ELSE
''
END AS xianxiakc,
CASE
WHEN tcc.THEACH_MODE > 0 THEN
''
ELSE
group_concat(tcc.COURSE_NAME)
END AS xianshangkc,
sum(integration) AS credit
FROM
(
SELECT
tc.OID AS classid,
tc.CREATEDATE AS CREATEDATE,
tc.CLASSNAME AS classname,
tc.trainMode AS trainMode,
tc.place AS place,
t1.THEACH_MODE,
t1.COURSE_NAME,
t1.integration
FROM
LMS_CLASS tc
LEFT JOIN LMS_CLASS_COURSE t1 ON t1.CLASS_ID = tc.OID
) tcc
GROUP BY
classid,
CREATEDATE,
classname,
trainMode,
place,
THEACH_MODE
) t0
GROUP BY
classid,
CREATEDATE,
classname,
trainMode,
place
结果如下，查询结果月0.88s，快了近1000倍
