MySQL - LEFT JOIN 与 GROUP_CONCAT 与 3 个表 - 未知列

Question

我正在尝试加入 3 个表并执行 GROUP_CONCAT，但是得到

Unknown column 'program_outcome.program_outcome_pk' in 'field list'

询问：

SELECT program_outcome.program_outcome_pk, 
       program_outcome.program_outcome, 
       GROUP_CONCAT(program_outcome_unit_outcome_lookup.unit_outcome_pk) unit_outcome_pks, 
       GROUP_CONCAT(unit_outcome.unit_outcome) unit_outcomes 
FROM   program_outcome po 
       LEFT JOIN program_outcome_unit_outcome_lookup pouo 
               ON po.program_outcome_pk = pouo.program_outcome_fk
       LEFT JOIN unit_outcome uo 
               ON pouo.unit_outcome_fk = uo.unit_outcome_pk 
GROUP  BY po.program_outcome_pk, 
          po.program_outcome

我正在寻找的结果是这样的：

+----------------------------------+--------------------------------------------------+
| program_outcome.program_outcome  |  unit_outcome.unit_outcome                       |
+----------------------------------+--------------------------------------------------+
| program outcome 1                | unit_outcome 2, unit_outcome 5                   |
| program outcome 2                | unit_outcome 7, unit_outcome 1                   |
| program outcome 3                | unit_outcome 1, unit_outcome 9, unit_outcome 11  |
+----------------------------------+--------------------------------------------------+

数据库小提琴

Answer 1

您需要使用您在from和join claues 中定义的别名：

SELECT po.program_outcome_pk, 
       po.program_outcome, 
       GROUP_CONCAT(pouo.unit_outcome_fk) unit_outcome_pks, 
       GROUP_CONCAT(uo.unit_outcome) unit_outcomes 
FROM   program_outcome po 
       LEFT JOIN program_outcome_unit_outcome_lookup pouo 
               ON po.program_outcome_pk = pouo.program_outcome_fk
       LEFT JOIN unit_outcome uo 
               ON pouo.unit_outcome_fk = uo.unit_outcome_pk 
GROUP  BY po.program_outcome_pk, 
          po.program_outcome

Answer 2

您可以删除别名，因为您的表没有冲突的名称，这是一个基于您的小提琴的有效查询：

SELECT program_outcome_pk, 
       program_outcome, 
       GROUP_CONCAT(unit_outcome_pk) unit_outcome_pks, 
       GROUP_CONCAT(unit_outcome) unit_outcomes 
FROM   program_outcome po 
       LEFT JOIN program_outcome_unit_outcome_lookup pouo 
               ON po.program_outcome_pk = pouo.program_outcome_fk
       LEFT JOIN unit_outcome uo 
               ON pouo.unit_outcome_fk = uo.unit_outcome_pk 
GROUP  BY po.program_outcome_pk, 
          po.program_outcome