通过Hibernate和PostgreSQL执行查询的差异导致PSQLException

Question

我想在Postgres 9.4数据库系统上使用版本4.2.21中的Hibernate通过JPA 2.0执行本机SQL查询.

基本上,根据我在stackoverflow上的最新帖子,我尝试将大量对象/记录放入"临时"桶中.

设置可以简化为以下设置,其中包含带有id字段和给定时间戳的表"MyObject":

CREATE TABLE myobject
(
  id bigint NOT NULL,
  lastseen timestamp without time zone, 
)

我应该执行查询的代码是这样的:

Query q = getEntityManager().createNativeQuery(
             "select count(id),date_part('day', :startDate - c.lastseen)  AS " +
             "difference from myobject c " +
             "group by date_part('day', :startDate - c.lastseen) order by difference asc");

q.setParameter("startDate", startDate);

List<Object[]> rawResults = q.getResultList();

//process the reuslts

通过pgAdmin3使用示例日期执行此查询将按预期返回结果.

但是,如果我尝试通过Hibernate执行相同的查询作为本机查询,它会失败并出现以下异常:

Caused by: org.postgresql.util.PSQLException:
FEHLER: column „myobject.lastseen“ must appear in the group by clause or be used in an aggregate function
  Position: 40
  at org.postgresql.core.v3.QueryExecutorImpl.receiveErrorResponse(QueryExecutorImpl.java:2270)
  at org.postgresql.core.v3.QueryExecutorImpl.processResults(QueryExecutorImpl.java:1998)
  at org.postgresql.core.v3.QueryExecutorImpl.execute(QueryExecutorImpl.java:255)
  at org.postgresql.jdbc2.AbstractJdbc2Statement.execute(AbstractJdbc2Statement.java:570)
  at org.postgresql.jdbc2.AbstractJdbc2Statement.executeWithFlags(AbstractJdbc2Statement.java:420)
  at org.postgresql.jdbc2.AbstractJdbc2Statement.executeQuery(AbstractJdbc2Statement.java:305)
  at org.hibernate.engine.jdbc.internal.ResultSetReturnImpl.extract(ResultSetReturnImpl.java:79)
  ... 94 more

这个异常似乎是有效且自我解释但为什么我可以通过PgAdmin3执行相同的查询？Hibernate SQL解析器比pgAdmin3更严格还是补偿了一些错误？

那么我的SQL查询如何制定以便通过Hibernate使其可执行？

编辑:

由于某种原因,以下SQL语句(带有显式子选择)通过PgAdmin3以及Hibernate工作:

select count(id), difference
from (select c.id,c.lastseen,date_part('day', :startDate - c.lastseen) AS difference
      from myobject c) AS temporalBucket
group by difference
order by difference asc

但是这仍然没有回答给定代码片段中先前查询的问题.

Answer 1

此查询也应该有效,没有子查询:

SELECT count(id)  -- or even better: count(*) AS ct
     , date_part('day', :startDate - c.lastseen) AS difference
FROM   myobject c 
GROUP  BY difference
ORDER  BY difference;

我怀疑的原因是:Hibernate使用预处理语句,并且两次出现:startDate作为两个参数传递.这样,Postgres不能假设两个表达式(在SELECT列表中和中GROUP BY)都是相同的......

使用等效的SQL命令PREPARE演示,这适用:

PREPARE test1 AS
SELECT count(*) AS ct
     , date_part('day', $1 - c.lastseen) AS difference
FROM   myobject c 
GROUP  BY date_part('day', $1 - c.lastseen)
ORDER  BY difference;

虽然这不是:

PREPARE test2 AS
SELECT count(*) AS ct
     , date_part('day', $1 - c.lastseen) AS difference
FROM   myobject c 
GROUP  BY date_part('day', $2 - c.lastseen)
ORDER  BY difference;

..并引发与你展示的相同的异常.

您可以使用我建议的查询先验地避免此问题.

有关:

• PostgreSQL在哪里计算条件