java - 同一张表上的左连接

Question

我正在使用 JPA 查询条件来构建一个在同一个表上进行联接的查询。该表如下所示。

Table A

Id  EventType        

A    Start                        
A    Start
A    End
B    Start
C    Start
C    End

我想找出相同 Id 的 EventType 为 Start 且没有 EventType End 的所有行。 在 SQL 中:我通过如下连接得到了这个:

   select DISTINCT *
     from (select *
             from A
            where Id='A'
              AND EventType = 'Start') startEventTable 
LEFT JOIN (select *
             from A
            where Id='A'
              AND EventType = 'endEvent') endEventTable 
       ON (startEventTable.Id = endEventTable.Id) 
    WHERE endEventTable.Id IS NULL;

我无法在 JPA 中实现这一点

CriteriaBuilder cb = entityManager.getCriteriaBuilder();
CriteriaQuery cq = cb.createQuery(A.class);
Root<A> r1 = cq.from(A.class);
SubQuery sq1 = cq.subquery(A.class);
SubQuery sq2 = cq.subquery(A.class);
Root<A> r2 = sql.from(A.class);
Root<A> r3 = sq2.from(A.class);
sq1.where(<predicate>);
sq2.where(<predicate>);

cq.where(cb.and(cb,exists(sq1), cb.exists(sq2).not()));
New TypedQuery(cq).getResultList();

此操作因多个路径异常而失败。我对 JPA 查询不熟悉，请在此处请求有人提供帮助。

Answer 1

使用以下更简单、更快的查询之一:

SELECT DISTINCT *  -- you probably don't need DISTINCT
FROM   A
WHERE  Id = 'A'
AND    EventType = 'Start'
AND    NOT EXISTS (
    SELECT 1
    FROM   A a1
    WHERE  a1.Id = A.Id
    AND    EventType = 'endEvent'
    );

或者

SELECT DISTINCT *  -- you probably don't need DISTINCT
FROM   A
LEFT   JOIN A a1 ON a1.Id = A.Id
                AND a1.EventType = 'endEvent'
WHERE  A.Id = 'A'
AND    A.EventType = 'Start'
AND    a1.Id IS NULL;

详细信息:

• Select rows which are not present in other table