couchdb - 通过CouchDB中的键返回唯一值

Question

有没有办法在CouchDB中执行以下操作？一种通过给定键返回唯一，不同值的方法？

SELECT DISTINCT field FROM table WHERE key="key1"

'key1' => 'somevalue'
'key1' => 'somevalue'
'key2' => 'anotherval'
'key2' => 'andanother'
'key2' => 'andanother'

例如:

http://localhost:5984/database/_design/designdoc/_view/distinctview?key=“key1”将返回['somevalue']

http://localhost:5984/database/_design/designdoc/_view/distinctview?key=“key2”将返回['anotherval'，'andanother']

Answer 1

As suggested in the CouchDB definitive guide，您应该将想要唯一的值放在键中，然后使用group=true查询reduce函数。

例如，假设keyfield是带有“key1”和“key2”的字段，而valuefield是带有值的字段，则您的 map 函数可能是:

function(doc) {
  // filter to get only the interesting documents: change as needed
  if (doc.keyfield && doc.valuefield) {
    /*
     * This is the important stuff:
     * 
     *  - by putting both, the key and the value, in the emitted key,
     *    you can filter out duplicates
     *    (simply group the results on the full key);
     * 
     *  - as a bonus, by emitting 1 as the value, you get the number
     *    of duplicates by using the `_sum` reduce function.
     */
    emit([doc.keyfield, doc.valuefield], 1);
  }
}

而您的reduce函数可能是:

_sum

然后用 group=true&startkey=["key2"]&endkey=["key2",{}]查询得到:

{"rows":[
{"key":["key2","anotherval"],"value":1},
{"key":["key2","andanother"],"value":2}
]}