Question

让我们说我经营一家弯曲的汽车公司。我们说我有下表： car_engine_mileage_counters这是car_engines到mileage_counters的联接表，同时还存储mileage的计算字段还可以说我在engine template上在工厂的引擎块级别编码系数。

UPDATE car_engine_mileage_counters
SET mileage = mileage_counters.mileage * coefficients.coefficient
FROM car_engines
INNER JOIN engine_templates
ON car_engines.template_id = engine_templates.id
INNER JOIN mileage_counters
ON mileage_counters.id = car_engine_mileage_counters.mileage_counter_id
INNER JOIN mileage_counter_templates
ON mileage_counter.template_id = mileage_counter_templates.id
INNER JOIN coefficients
ON coefficients.mileage_counter_template_id = mileage_counter_templates.id
WHERE coefficients.engine_template_id = engine_template.id AND car_engines.id = car_engine_mileage_counters.engine_id;

这个（显然是虚构的）示例失败了：

错误：对表的FROM子句条目的无效引用＆＃34; car_engine_mileage_counters＆＃34; LINE 7：ON mileage_counters.id = car_engine_mileage_counters ... ^ 提示：表＆＃34; measure_instances_question_instances＆＃34;有一个条目，但不能引用从这部分查询。

枚举单个FROM子句中的所有表格，并使用WHERE AND代替所有INNER JOIN但是效果正常。

我的问题是，为什么？内连接查询有什么问题？我该如何解决？这有关系吗？

Answer 1

UPDATE cem
SET mileage = mileage_counters.mileage * coefficients.coefficient
FROM car_engine_mileage_counters cem
INNER JOIN car_engines 
ON car_engines.id = cem.engine_id
INNER JOIN engine_templates
ON car_engines.template_id = engine_templates.id
INNER JOIN mileage_counters
ON mileage_counters.id = cem.mileage_counter_id
INNER JOIN mileage_counter_templates
ON mileage_counter.template_id = mileage_counter_templates.id
INNER JOIN coefficients
ON coefficients.mileage_counter_template_id = mileage_counter_templates.id
WHERE coefficients.engine_template_id = engine_template.id AND car_engines.id = cem.engine_id;

为什么在多个where子句的情况下，Inner Join查询不起作用

1 个答案: