Question

我使用JPA查询条件在同一个表上构建一个带连接的查询。该表如下所示。

Table A

Id  EventType        

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

我想查找EventType为Start且没有相同Id的EventType End的所有行。在SQL中：我通过下面的连接得到了这个：

   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;

我在JPA中无法实现这一点

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();

这会因多个路径异常而失败。我是JPA查询的新手，请求有人在这里提供帮助。

Answer 1

您可以在JPA中表达等效查询：

SELECT *
FROM A
WHERE Id='A' AND EventType = 'Start'
  AND Id NOT IN (
        SELECT Id from A
        WHERE Id='A'
          AND EventType = 'endEvent')

使用this方法。

Answer 2

使用以下更简单，更快速的查询之一：

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;

详细说明：

Select rows which are not present in other table

左连接在同一个表上

2 个答案: