Question

我有以下观点：

function (doc, meta) {
  if (meta.type == "json")
  if ( doc.id 
      && doc.id.root.indexOf("1.2.250.1.199.16.1.1") == 0 
      && doc.setId
      && doc.versionNumber)
  {
    emit(doc.setId.extension, parseInt(doc.versionNumber.value))
  }
}

返回以下结果集：

Key Value
"4816f76e-33f9-456a-9e23-961799883994" 1
wound2QualificationRev1

"4816f76e-33f9-456a-9e23-961799883994" 2
wound2QualificationRev2

现在我想将最大值的结果集限制为仅返回

Key Value
"4816f76e-33f9-456a-9e23-961799883994" 2
wound2QualificationRev2

我如何修改视图？使用自定义reduce方法？

编辑1 ：请注意，此处显示的结果集是部分的。我无法使用orderby和limit来实现我的目标。

Answer 1

我不知道Couchbase，但是写一些像：

 emit(parseInt(doc.versionNumber.value),doc.setId.extension)

然后用：

查询它

?descending=true&&limit=1

你也可以使用map reduce：How to calculate Max value using Map-Reduce in CouchDB?，或者考虑使用N1QL，它实现了MIN和MAX SQL查询

Answer 2

Kudos 到@Leogiciel的Max reduce功能，我终于找到了解决方案。首先，视图定义保持不变。解决方案是使用Max reduce function的这种实现，最重要的是使用查询参数 group和reduce 。

初始结果集，此处显示为原始Json：

{"total_rows":9,"rows":[
{"id":"wound1Image1","key":"0a41d087-1a7f-4d9f-8df9-83d0deb2566c","value":1},
{"id":"wound2QualificationRev1","key":"4816f76e-33f9-456a-9e23-961799883994","value":1},
{"id":"wound2QualificationRev2","key":"4816f76e-33f9-456a-9e23-961799883994","value":2},
{"id":"wound2Image3","key":"65ff979a-e1e0-43d4-a24f-a3ee0cc8b67c","value":1},
{"id":"wound2Image1","key":"69f29cf8-3ee7-4681-937d-d465edc9bb16","value":1},
{"id":"wound1Image2","key":"76ab9a67-a17b-4fc6-a105-60b57e971d4f","value":1},
{"id":"wound1Synthesis","key":"bc1a7ec0-30d7-4493-8dd9-dcf6d0b48cc9","value":1},
{"id":"wound1Qualification","key":"cb375a5f-e07d-449a-ab13-60dba16a0323","value":1},
{"id":"wound2Image2","key":"dfb5e7eb-6192-46ba-84d2-0e5996536930","value":1}
]
}

使用以下查询参数：

?group=true&reduce=true

返回正确的结果集：

{"rows":[
{"key":"0a41d087-1a7f-4d9f-8df9-83d0deb2566c","value":1},
{"key":"4816f76e-33f9-456a-9e23-961799883994","value":2},
{"key":"65ff979a-e1e0-43d4-a24f-a3ee0cc8b67c","value":1},
{"key":"69f29cf8-3ee7-4681-937d-d465edc9bb16","value":1},
{"key":"76ab9a67-a17b-4fc6-a105-60b57e971d4f","value":1},
{"key":"bc1a7ec0-30d7-4493-8dd9-dcf6d0b48cc9","value":1},

{"key":"cb375a5f-e07d-449a-ab13-60dba16a0323","value":1},    {"key":"dfb5e7eb-6192-46ba-84d2-0e5996536930","value":1}
]
}

如何选择最大值的记录？

2 个答案: