jpql - JPQL order by expression 子句：ORDER BY (x = y) ASC

Question

我正在尝试通过相等表达式对查询结果进行排序，例如

   ORDER BY (x = y) ASC

但我不断得到意想不到的令牌=。我什至尝试过像

   ORDER BY COUNT(x = y) ASC

但也没有成功：expecting CLOSE, found '='

有没有办法通过 JPQL 实现这一目标？谢谢

Answer 1

不，它不适用于 JPQL。这是不可能的，因为

1. x=y不可订购
2. x=y不是 SELECT 子句的一部分。

在 JPA 2.0 规范中，这是用以下词语来说明的：

An orderby_item must be one of the following:

1. A state_field_path_expression that evaluates to an orderable state field 
   of an entity or embeddable class abstract schema type designated in the 
   SELECT clause by one of the following:
     • a general_identification_variable
     • a single_valued_object_path_expression

2. A state_field_path_expression that evaluates to the same state field of 
   the same entity or embeddable abstract schema type as a      
   state_field_path_expression in the SELECT clause

3. A result_variable that refers to an orderable item in the SELECT clause 
   for which the same result_variable has been specified. This may be the 
   result of an aggregate_expression, a scalar_expression, or a 
   state_field_path_expression in the SELECT clause.

您可以尝试在 SELECT 子句中使用 CASE 来构造数字属性并在 ORDER BY 中使用它。