相当于 HQL 中的 GREATEST()答案

【问题标题】：Equivalent of GREATEST() in HQL相当于 HQL 中的 GREATEST()
【发布时间】：2019-10-20 00:21:07
【问题描述】：

我正在尝试在 HQL 中查找两个日期中最大的一个。

在 SQL 中这是有效的：

SELECT ( GREATEST(a1.startDate, '2019-10-01T00:00:00Z') ) FROM Activity AS a1 WHERE a1.id = 66232

但是 HQL 中的等价物给了我以下错误：

java.lang.IllegalArgumentException: org.hibernate.QueryException: No data type for node: org.hibernate.hql.internal.ast.tree.MethodNode 
 \-[METHOD_CALL] MethodNode: '('
    +-[METHOD_NAME] IdentNode: 'GREATEST' {originalText=GREATEST}
    \-[EXPR_LIST] SqlNode: 'exprList'
       +-[NAMED_PARAM] ParameterNode: '?' {name=param0, expectedType=null}
       \-[NAMED_PARAM] ParameterNode: '?' {name=param1, expectedType=null}
 [SELECT GREATEST(:param0,:param1) FROM xxx.xxx.xxx.Activity AS a1 WHERE a1.id = :param2]
    at org.hibernate.internal.ExceptionConverterImpl.convert(ExceptionConverterImpl.java:133)
    at org.hibernate.internal.ExceptionConverterImpl.convert(ExceptionConverterImpl.java:157)
    at org.hibernate.internal.ExceptionConverterImpl.convert(ExceptionConverterImpl.java:164)
    ... 134 more

有没有办法在 HQL 中使用两个日期来实现与 MySQL 的 GREATEST() 相同的功能？

编辑：我也尝试使用 CASE WHEN ... THEN ... ELSE ... END 但最终出现以下错误：

java.lang.IllegalArgumentException: org.hibernate.QueryException: No data type for node: org.hibernate.hql.internal.ast.tree.SearchedCaseNode 
 \-[CASE] SearchedCaseNode: 'CASE'
    +-[WHEN] SqlNode: 'WHEN'
    |  +-[GT] BinaryLogicOperatorNode: '>'
    |  |  +-[NAMED_PARAM] ParameterNode: '?' {name=param0, expectedType=null}
    |  |  \-[NAMED_PARAM] ParameterNode: '?' {name=param1, expectedType=null}
    |  \-[NAMED_PARAM] ParameterNode: '?' {name=param2, expectedType=null}
    \-[ELSE] SqlNode: 'ELSE'
       \-[NAMED_PARAM] ParameterNode: '?' {name=param3, expectedType=null}
 [SELECT CASE WHEN :param0 > :param1 THEN :param2 ELSE :param3 END  FROM flowzone.model.activity.Activity AS a1 WHERE a1.id = :param4]
    at org.hibernate.internal.ExceptionConverterImpl.convert(ExceptionConverterImpl.java:133)
    at org.hibernate.internal.ExceptionConverterImpl.convert(ExceptionConverterImpl.java:157)
    at org.hibernate.internal.ExceptionConverterImpl.convert(ExceptionConverterImpl.java:164)
    ... 138 more

【问题讨论】：

标签： mysql hql

【解决方案1】：

MySQL 手册将GREATEST() 解释为

GREATEST(value1,value2,...)

有两个或多个参数，返回最大的（最大值）论据。

所以 MySQL 的 GREATEST(value1,value2,...) 函数/语法糖应该和下面的 MySQL 语法相同..

SELECT 
 MAX(greatest.v)
FROM (
  SELECT value1 AS v
  UNION ALL
  SELECT value2 AS v
  [, UNION ALL SELECT ...]
) AS greatest

不确定它是否是 HQL 证明，但也许是下面的查询？

SELECT 
 MAX(alias.startDate)
FROM (
  SELECT a1.startDate FROM Activity AS a1 WHERE a1.id = 66232
  UNION ALL
  SELECT CAST('2019-10-01 00:00:00' AS DATETIME) AS startDate
) AS alias

【讨论】：