新手求sql query
一个table, x, y, z 3个字段， 求y-z的最大值所对应的x值,

自己写了query，不过有错误

select temp.a
from  
  (select x a,abs(y-z) b
  from table t
  where z in
  (SELECT z FROM `t` WHERE z > 0)  
  group by x) temp
where temp.b in (select max(b) from temp)

提示 table.temp 不存在

本人初学，还望高手们多多指点



------解决方案--------------------
select temp.a
from
(select x a,abs(y-z) b
from table t
where z in
(SELECT z FROM `t` WHERE z > 0)
group by x) temp
where temp.b in (select max(b) from (select x a,abs(y-z) b
from table t
where z in
(SELECT z FROM `t` WHERE z > 0)
group by x) temp1)