# The problem when using cardinality aggs!

**URL:** <https://discuss.elastic.co/t/the-problem-when-using-cardinality-aggs/76140>\
**Category:** Elasticsearch\
**Created:** [February 23, 2017, 3:46am UTC](https://discuss.elastic.co/t/the-problem-when-using-cardinality-aggs/76140 "2017-02-23T03:46:24Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![a943013827](https://avatars.discourse-cdn.com/v4/letter/a/f475e1/32.png) [@a943013827](https://discuss.elastic.co/u/a943013827)\
**Post date:** [February 23, 2017, 3:46am UTC](https://discuss.elastic.co/t/the-problem-when-using-cardinality-aggs/76140/1 "2017-02-23T03:46:24Z")

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I have a dataset with the mapping:  
ad : long  
tk : long  
ts : date

I index some docs every hour and these docs have follow features:  
ad: always be 999999  
tk :Randomly fetches a value from a list of length 10  
ts: current timestamp

when I using filter aggs on 'ad':  
query1:  
`{ 'aggs': {'app_aggs': {'filter': {'term':{'ad':999999}}, 'aggs': {'date_aggs': {'date_histogram': {'field': 'ts', 'interval': 'day', 'time_zone': '+08:00', 'format': 'yyyy-MM-dd HH:mm:ss'}, 'aggs': {'uv_aggs': {'cardinality': {'field': 'tk'}}}}}}}}`  
result1:  
{u'app\_aggs': {u'date\_aggs': {u'buckets': [{u'uv\_aggs': **{u'value': 10}** , u'key\_as\_string': u'2017-02-12 00:00:00', u'key': 1486828800000, u'doc\_count': 5176}]}, **u'doc\_count': 5176** }}

Its ok that I have 10 values of tk.

But when I using term aggs on 'ad':  
query2:  
`{ 'aggs': {'app_aggs': {'terms': {'field': 'ad'}, 'aggs': {'date_aggs': {'date_histogram': {'field': 'ts', 'interval': 'day', 'time_zone': '+08:00', 'format': 'yyyy-MM-dd HH:mm:ss'}, 'aggs': {'uv_aggs': {'cardinality': {'field': 'tk'}}}}}}}}`

result2:  
{u'app\_aggs': {u'buckets': [{u'date\_aggs': {u'buckets': [{u'uv\_aggs': **{u'value': 8}** , u'key\_as\_string': u'2017-02-12 00:00:00', u'key': 1486828800000, **u'doc\_count': 5176** }]}, u'key': 999999, u'doc\_count': 5176}], u'sum\_other\_doc\_count': 0, u'doc\_count\_error\_upper\_bound': 0}}

Why it reduce to 8 ??

then I replace the "cardinality":"tk" to "terms":"tk":

query:  
`{ 'aggs': {'app_aggs': {'terms': {"field":"ad"}, 'aggs': {'date_aggs': {'date_histogram': {'field': 'ts', 'interval': 'day', 'time_zone': '+08:00', 'format': 'yyyy-MM-dd HH:mm:ss'}, 'aggs': {'uv_aggs': {'terms': {'field': 'tk'}}}}}}}}`

result:  
{u'app\_aggs': {u'buckets': [{u'date\_aggs': {u'buckets': [{u'uv\_aggs': {u'buckets': [{u'key': 96741171783034867, u'doc\_count': 545}, {u'key': 125100716348049356, u'doc\_count': 537}, {u'key': 82496289943871922, u'doc\_count': 522}, {u'key': 79031552758613517, u'doc\_count': 521}, {u'key': 109651577186779136, u'doc\_count': 520}, {u'key': 75733601942997721, u'doc\_count': 517}, {u'key': 125602239551986866, u'doc\_count': 513}, {u'key': 115378095770568369, u'doc\_count': 511}, {u'key': 126639628788471066, u'doc\_count': 505}, {u'key': 121104902114270720, u'doc\_count': 485}], u'sum\_other\_doc\_count': 0, u'doc\_count\_error\_upper\_bound': 0}, u'key\_as\_string': u'2017-02-12 00:00:00', u'key': 1486828800000, u'doc\_count': 5176}]}, u'key': 999999, **u'doc\_count': 5176** }], u'sum\_other\_doc\_count': 0, u'doc\_count\_error\_upper\_bound': 0}}

It does exist 10 buckets of "tk" ！！！  
why cardinality aggreration gives the wrong result??

the elasticsearch version is 2.4.2

Any advice is helpful,thank you.

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<div class="post-metadata">

**Author:** ![warkolm](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/warkolm/32/39224_2.png) [@warkolm](https://discuss.elastic.co/u/warkolm)\
**Post date:** [February 24, 2017, 10:03am UTC](https://discuss.elastic.co/t/the-problem-when-using-cardinality-aggs/76140/2 "2017-02-24T10:03:21Z")

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What's the cardinality of the data like?  
See [https://www.elastic.co/guide/en/elasticsearch/reference/2.4/search-aggregations-metrics-cardinality-aggregation.html#\_counts\_are\_approximate](https://www.elastic.co/guide/en/elasticsearch/reference/2.4/search-aggregations-metrics-cardinality-aggregation.html#_counts_are_approximate)

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**Author:** ![system](https://us1.discourse-cdn.com/elastic/original/3X/1/a/1ac57faf039f6b580b3f104ef42a2a89e41014de.png) [@system](https://discuss.elastic.co/u/system)\
**Post date:** [March 24, 2017, 10:03am UTC](https://discuss.elastic.co/t/the-problem-when-using-cardinality-aggs/76140/3 "2017-03-24T10:03:49Z")

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