MySQL在'中加入未知列；关于第'条；

我目前正在尝试两次加入同一个表

我有一张类似于下面的表格：

行程：

还有另一个表，其中包含这些位置的值：

地点：

location_code (pk)
location

我正在尝试根据trip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;

让我想到：

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

---

在这一点上，我很确定我有一些理解不正确的地方，我将非常感谢您的帮助。

这是因为您的alisas的名称与您使用的名称不同

改变

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

到

---

这是因为alisas的名称与您使用的名称不同

改变

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

到

---

这是因为alisas的名称与您使用的名称不同

改变

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

到

---

这是因为alisas的名称与您使用的名称不同

改变

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

到

---

在on子句中，按您提供的别名（leavingloc或arrivalloc）而不是按“locations”引用“locations”表在on子句中，按您提供的别名（leavingloc或arrivalloc）而不是按on子句中的“locations”引用“locations”表，在on子句中，按您给的别名（leavingloc或arrivalloc）而不是按“locations”引用“locations”表，在join子句中按您给的别名（leavingloc或arrivalloc）而不是按“locations”引用“locations”表，所以mysql变得很困惑：

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;

---

您给表添加了别名，但没有在join子句中使用别名，因此mysql感到困惑：

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;

---

您给表添加了别名，但没有在join子句中使用别名，因此mysql感到困惑：

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;

---

您给表添加了别名，但没有在join子句中使用别名，因此mysql感到困惑：

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;

---

我现在明白我的错误了。非常感谢。我现在明白我的错误了。非常感谢。我现在明白我的错误了。非常感谢。我现在明白我的错误了。非常感谢你