Question

我目前正在尝试两次加入同一张桌子。

我有一张类似于下面的表格：

跳闸：

arrival_loc_code
leaving_loc_code

还有另一个表格，其中包含这些位置的值：

位置：

location_code (pk)
location

我试图根据行程中的位置代码获取到达和离开的位置。我目前的尝试导致：

select leavingloc.location,arrivalloc.location from trip 
    join locations as leavingloc on trip.departureloccode = locations.locationcode 
    join locations as arrivalloc on trip.arrivalloccode = locations.locationcode;

导致我：

ERROR 1054 (42S22): Unknown column 'locations.locationcode' in 'on clause'

在这一点上，我非常确定我有一些错误的理解，并希望得到任何帮助。

Answer 1

你给表别名但后来没有使用join子句中的别名，所以mysql变得混乱：

select leavingloc.location, arrivalloc.location from trip 
    join locations as leavingloc on trip.departureloccode = leavingloc.locationcode 
    join locations as arrivalloc on trip.arrivalloccode = arrivalloc.locationcode;

Answer 2

这是因为您的alisas名称与您使用的名称不同。

更改

   join locations as leavingloc on trip.departureloccode = locations.locationcode 
    join locations as arrivalloc on trip.arrivalloccode = locations.locationcode;

要

 join locations as leavingloc on trip.departureloccode = leavingloc.locationcode 
    join locations as arrivalloc on trip.arrivalloccode = arrivalloc.locationcode;

Answer 3

在您的on子句中，请参阅＆＃39;位置＆＃39;你给他们的别名（leavingloc或arrivalloc）而不是＆＃39;位置＆＃39;

的表格

MySQL在＆＃39; on子句＆＃39;中加入未知列

3 个答案: