如何使用JPA Criteria API / Hibernate按Case语句分组

Question

我正在尝试执行以下查询，并通过一个case语句进行选择，并通过同一case语句进行分组。

Select USER, 
  (CASE
    WHEN value between 0 AND 2 then '0-2'
    WHEN value between 3 AND 4 then '3-4'
    ELSE '5+'
  END) as CASE_STATEMENT ,
SUM(value)
.....
Group by user, CASE_STATEMENT

与Hibernate一起使用JPA 2.0 Criteria API。

我的测试用例看起来像...

    CriteriaBuilder cb = em.getCriteriaBuilder()
    CriteriaQuery cq = cb.createQuery(Tuple)
    def root = cq.from(TestEntity)
    def userGet = root.get('user')
    def valueGet = root.get('value')
    def caseExpr =
            cb.selectCase()
                .when(cb.between(valueGet, 0, 2), '0-2')
                .when(cb.between(valueGet, 3, 4), '3-4')
                .otherwise('5+')
    def sumExpr = cb.sum(valueGet)

    cq.multiselect([userGet, caseExpr, sumExpr])
    cq.groupBy([userGet, caseExpr])
    log(typedQuery.unwrap(Query).queryString)
    List<Tuple> tuples = typedQuery.getResultList()

queryString的日志语句读取

SELECT generatedAlias0.USER, 
   CASE 
     WHEN generatedAlias0.value BETWEEN 0 AND 2 THEN Cast(:param0 AS STRING) 
     WHEN generatedAlias0.value BETWEEN 3 AND 4 THEN Cast(:param1 AS STRING) 
     ELSE Cast(:param2 AS STRING) 
   END, 
   Sum(generatedAlias0.value) 
FROM   test AS generatedAlias0 
GROUP  BY generatedAlias0.USER, 
      CASE 
        WHEN generatedAlias0.value BETWEEN 0 AND 2 THEN Cast( 
        :param3 AS STRING) 
        WHEN generatedAlias0.value BETWEEN 3 AND 4 THEN Cast( 
        :param4 AS STRING) 
        ELSE Cast(:param5 AS STRING) 
      END 

调用typedQuery.getResultList（）时，出现以下错误声明

javax.persistence.PersistenceException: org.hibernate.exception.GenericJDBCException: could not extract ResultSet

Caused by: org.h2.jdbc.JdbcSQLException: Column "TESTENTITY0_.VALUE" must be in the GROUP BY list; SQL statement:

select testentity0_.user as col_0_0_, case when testentity0_.value between 0 and 2 then cast(? as varchar(255)) when testentity0_.value between 3 and 4 then cast(? as varchar(255)) else cast(? as varchar(255)) end as col_1_0_, sum(testentity0_.value) as col_2_0_ from test testentity0_ group by testentity0_.user , case when testentity0_.value between 0 and 2 then cast(? as varchar(255)) when testentity0_.value between 3 and 4 then cast(? as varchar(255)) else cast(? as varchar(255)) end [90016-194]

我尝试按表达式分组的方式有问题吗？我也尝试过按别名和数字文字（1、2）分组

我还有另一种方法可以构造SQL以获得相同的结果吗？

谢谢。

Answer 1

正如异常消息所示，问题与 DBMS 级别的语句有关Group By。请参阅： https: //www.percona.com/blog/2019/05/13/solve-query-failures-regarding-only_full_group_by-sql-mode/

要解决该错误，您必须

• Group By Mode将底层 DBMS 的设置为限制性较小的级别（MySQL 允许禁用 only-full-group-by，但H2 不允许（您可以尝试MODE=MYSQL在 jdbc 连接字符串中设置）

  或更好）

• 将属于 select 语句一部分的所有列添加到该GROUP BY语句或聚合函数中，如上所述。

  您应该能够构建满足 GROUP BY RESTRICTIONS 的嵌套查询。

  为了救援，有一些（可能是 DBMS 特定的）聚合函数（至少在MySQL中）。为了欺骗 JPA 和 Hibernate 理解这些，有多种方法可以实现这一点，如 https://vladmihalcea.com/hibernate-sql-function-jpql-criteria-api-query/ 和 https://vladmihalcea.com中所述。 /the-jpa-entitymanager-createnativequery-is-a-magic-wand/

编辑

与上述陈述相反和补充，经过以下讨论后的发现是：

• 该异常是由类中的h2 驱动程序org.h2.expression.ExpressionColumn在验证查询语法时引发的
• 该解决方案需要在查询中设置和引用别名（在case 语句或子查询处），这在Criteria API中目前是不可能的（请参阅列别名通常不能在查询本身中引用）
• 解决方法是创建一个像这样的 NativeQuery：

List<Tuple> tuples = em.createNativeQuery(
"SELECT generatedAlias0.USER, " +
"   CASE " +
"     WHEN generatedAlias0.value BETWEEN 0 AND 2 THEN Cast(:param0 AS VARCHAR) " +
"     WHEN generatedAlias0.value BETWEEN 3 AND 4 THEN Cast(:param1 AS VARCHAR) " +
"     ELSE Cast(:param2 AS VARCHAR) " +
"   END c, " +
"   Sum(generatedAlias0.value) as sumvalue " +
"FROM test AS generatedAlias0 " +
"GROUP  BY generatedAlias0.USER, c "
)
.setParameter("param0", "0-2")
.setParameter("param1", "3-4")
.setParameter("param2", "5+")
.getResultList();