FIND_IN_SET的使用，前面介绍过，distinct是结果去重复的函数，两者结合使用，却花费了我一天的光阴。
1、先面试含有重复值正确的显示顺序
select lId
from tbCourse1 as a left join tbCourseClassify as b
on a.lId=b.lCourseId
where (a.nUserType=1 or a.nUserType=0) and a.strServiceids like '%.0.%'
and b.nType in (-1,10,9,11,12,18,19,32,1,2,3,4,5,6,7,8,52,53,54,55,56,57,102,103,104,105,106,110,111,109,112,113)
ORDER BY FIND_IN_SET(b.nType,'-1,10,9,11,12,18,19,32,1,2,3,4,5,6,7,8,52,53,54,55,56,57,102,103,104,105,106,110,111,109,112,113')
,b.lOrderIdx desc
2、不含重复值的结果集，顺序已经被distinct(暂且归给distinct)打乱
select distinct(lId)
from tbCourse1 as a left join tbCourseClassify as b
on a.lId=b.lCourseId
where (a.nUserType=1 or a.nUserType=0) and a.strServiceids like '%.0.%'
and b.nType in (-1,10,9,11,12,18,19,32,1,2,3,4,5,6,7,8,52,53,54,55,56,57,102,103,104,105,106,110,111,109,112,113)
ORDER BY FIND_IN_SET(b.nType,'-1,10,9,11,12,18,19,32,1,2,3,4,5,6,7,8,52,53,54,55,56,57,102,103,104,105,106,110,111,109,112,113')
,b.lOrderIdx desc
3、最终正确的结果
select DISTINCT(lId) from(
select lId
from tbCourse1 as a left join tbCourseClassify as b
on a.lId=b.lCourseId
where (a.nUserType=1 or a.nUserType=0) and a.strServiceids like '%.0.%'
and b.nType in (-1,10,9,11,12,18,19,32,1,2,3,4,5,6,7,8,52,53,54,55,56,57,102,103,104,105,106,110,111,109,112,113)
ORDER BY FIND_IN_SET(b.nType,'-1,10,9,11,12,18,19,32,1,2,3,4,5,6,7,8,52,53,54,55,56,57,102,103,104,105,106,110,111,109,112,113')
,b.lOrderIdx desc) as c