MySQL - LEFT JOIN 與 GROUP_CONCAT 與 3 個表 - 未知列

Question

我正在嘗試加入 3 個表並執行 GROUP_CONCAT，但是得到

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

詢問：

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

我正在尋找的結果是這樣的：

+----------------------------------+--------------------------------------------------+
| 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  |
+----------------------------------+--------------------------------------------------+

數據庫小提琴

Answer 1

您需要使用您在from和join claues 中定義的別名：

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

您可以刪除別名，因為您的表沒有沖突的名稱，這是一個基於您的小提琴的有效查詢：

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