UNION 语句中的 MySQL SELECT 无法引用父表

Question

我正在尝试执行以下 MySQL SELECT 语句，以获取针对每个父机会 ID 完成的最后一次活动的日期。

活动列表将从 4 个表中检索：通话、会议、任务、电子邮件。

当我添加条件“XXXXX.parent_id = chance.id”（在内部 4 个子 SELECTS 中）时，出现语法错误。

如果我删除“XXXXX.parent_id = chance.id”，语句就会被执行（当然，结果与我想要的无关）。

这是我尝试过的代码：

SELECT
opportunities.id,
opportunities.name,
(
    SELECT MAX(`last_activity_date`) FROM
        (
        SELECT c.date_end AS `last_activity_date`     
        FROM calls AS c     
        WHERE c.parent_type = 'Opportunities'      
        AND c.parent_id = opportunities.id      
        AND c.status IN ('Held')      
        AND c.deleted = '0'     

        UNION

        SELECT m.date_end     
        FROM meetings AS m     
        WHERE m.parent_type = 'Opportunities'      
        AND m.parent_id = opportunities.id      
        AND m.status IN ('Held')      
        AND m.deleted = '0'     

        UNION

        SELECT t.date_due     
        FROM tasks AS t     
        WHERE t.parent_type = 'Opportunities'      
        AND t.parent_id = opportunities.id      
        AND t.status IN ('Completed')      
        AND t.deleted = '0'     

        UNION

        SELECT e.date_sent     
        FROM emails AS e     
        WHERE e.parent_type = 'Opportunities'      
        AND e.parent_id = opportunities.id      
        AND e.status IN ('sent', 'archived')      
        AND e.deleted = '0'    
    ) AS `activities`  
) AS "opportunities_activities"     

FROM opportunities   
WHERE opportunities.deleted = '0'     
ORDER BY opportunities.id ASC

Answer 1

您不能在内部嵌套查询中使用外部查询字段，因为每个内部查询都必须独立于任何外部查询。

尝试下面的查询以获得所需的结果。

SELECT
opportunities.id,
opportunities.name,
(
    SELECT MAX(`last_activity_date`) FROM
        (
        SELECT c.date_end AS `last_activity_date`     
        FROM calls AS c     
        join opportunities o on c.parent_id = o.id
        WHERE c.parent_type = 'Opportunities'      
        AND c.status IN ('Held')      
        AND c.deleted = '0'     

        UNION

        SELECT m.date_end     
        FROM meetings AS m     
        join opportunities o on m.parent_id = o.id
        WHERE m.parent_type = 'Opportunities'           
        AND m.status IN ('Held')      
        AND m.deleted = '0'     

        UNION

        SELECT t.date_due     
        FROM tasks AS t 
        join opportunities o on t.parent_id = o.id    
        WHERE t.parent_type = 'Opportunities'      
        AND t.status IN ('Completed')      
        AND t.deleted = '0'     

        UNION

        SELECT e.date_sent     
        FROM emails AS e  
        join opportunities o on e.parent_id = o.id
        WHERE e.parent_type = 'Opportunities'      
        AND e.status IN ('sent', 'archived')      
        AND e.deleted = '0'    
    ) AS `activities`  
) AS "opportunities_activities"     

FROM opportunities   
WHERE opportunities.deleted = '0'     
ORDER BY opportunities.id ASC