我的route表中有四个字段busid, routid, position and distance
我想显示busid and distance from a select query。我的选择查询如下：
$endb = mysql_query("select case when a.position < b.position then a.busid when a.position > b.position then a.busid else null end as busid, a.distance as distance from (select busid,position from route where routid=$result2) a join (select busid,position from route where routid=$end) b on a.busid = b.busid") or die(mysql_error());
但是当我使用此查询时，它给出了错误：
unknown field distance in field list。请帮助我所缺少的 最佳答案
子查询a中缺少距离
select
case
when a.position < b.position then a.busid
when a.position > b.position then a.busid
else null
end as busid,
a.distance as distance
from (
select busid, position, distance
from route
where routid=$result2
) as a join (
select busid, position
from route
where routid=$end
) as b
on a.busid = b.busid
甚至更好的版本：
SELECT if (a.position <> b.position, a.busid, null) busid, a.distance
FROM route a, route b
WHERE a.busid = b.busid
AND a.routid= $result2
AND b.routid= $end