SQL - 根据不同的属性获取任何行，不重复 [英] SQL - Fetch any rows based on a distinct property, no duplicates

问题描述

是否有可能运行一个查询，该查询表示为该表提取所有具有不同属性的表，并为该不同属性选择任何匹配的行，这对于基于一个属性的唯一/不同行无关紧要。

如果

  row1：name：a，age：10，街道：james street 
 row2：name：b，age：15，street：peter street 
 row3：name：c，age：17，street：james street 
  

现在我希望查询返回

  row2和row1或row2 
  

无论是row1还是row2，不在乎。

现在，理想情况下我想使用hibernate标准查询来执行此操作，因为我已经有了一个查询生成器，并且我只是将其添加为一个选项。

解决方案

您可以尝试投影： http://docs.jboss.org/hibernate/orm/3.3/reference/en/html/querycriteria.html#querycriteria-预测

类似这样的工作可能会奏效。它将根据街道属性选择唯一的结果：

 列出结果= session.createCriteria（Entity.class）
 .setProjection（Projections.projectionList（）
 .add（Projections.distinct（Projections.property（street）））
）
 .list（）; 
  

Is it possible to run a query, that says fetch all for this table that have distinct property and select any matched row for that distinct property, doesn't matter to unique/distinct rows based on just one property.

If

row1 : name:a, age:10, street:james street
row2 : name:b, age:15, street:peter street
row3 : name:c, age:17, street:james street

Now I would like the query to return

row2 and either row1 or row2 

Doesn't matter if it is row1 or row2, i don't care.

Now, ideally i'd like to perform this using hibernate criteria queries because I already have a query builder for that and I am just adding this as an option.

解决方案

You could try Projections: http://docs.jboss.org/hibernate/orm/3.3/reference/en/html/querycriteria.html#querycriteria-projection

Something like this could work. It will select unique results based on "street" property:

List results = session.createCriteria(Entity.class)
    .setProjection( Projections.projectionList()
        .add(Projections.distinct(Projections.property("street")))
    )
    .list();

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