mysql - 左连接未知列

Question

我在“on 子句”中得到未知列“assessment_assessment_type_lookup.assessment_type_fk”，查询如下。表格和列是正确的。

SELECT * FROM assessment
LEFT JOIN assessment_type 
ON assessment_type.assessment_type_pk = assessment_assessment_type_lookup.assessment_type_fk
LEFT JOIN assessment as ass
ON ass.assessment_pk = assessment_assessment_type_lookup.assessment_fk
LEFT JOIN unit_outcome
ON unit_outcome.unit_outcome_pk = unit_unit_outcome_lookup.unit_outcome_fk
LEFT JOIN unit
ON unit.unit_pk = unit_unit_outcome_lookup.unit_fk
LEFT JOIN unit_outcome as uo
ON uo.unit_outcome_pk = unit_outcome_assessment_lookup.unit_outcome_fk
LEFT JOIN assessment as ass2
ON ass2.assessment_pk = unit_outcome_assessment_lookup.assessment_fk
AND unit.unit_pk = '$unit_pk' GROUP BY assessment.assessment_pk

标签： mysql

Answer 1

您正在尝试通过无法完成的 tableassessment_type_lookup加入评估和评估类型。

如果您希望连接 2 个表，则必须在它们的ON子句中同时使用它们。