druid/docs/content/SegmentMetadataQuery.md

---
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---
Segment metadata queries return per segment information about:
\* Cardinality of all columns in the segment
\* Estimated byte size for the segment columns in TSV format
\* Interval the segment covers
\* Column type of all the columns in the segment
\* Estimated total segment byte size in TSV format
\* Segment id

    <code>{
      "queryType":"segmentMetadata",
      "dataSource":"sample_datasource",
      "intervals":["2013-01-01/2014-01-01"],
    }
    </code>

There are several main parts to a segment metadata query:

|property|description|required?|
|--------|-----------|---------|
|queryType|This String should always be “segmentMetadata”; this is the first thing Druid looks at to figure out how to interpret the query|yes|
|dataSource|A String defining the data source to query, very similar to a table in a relational database|yes|
|intervals|A JSON Object representing ISO-8601 Intervals. This defines the time ranges to run the query over.|yes|
|merge|Merge all individual segment metadata results into a single result|no|
|context|An additional JSON Object which can be used to specify certain flags.|no|

The format of the result is:

    <code>[ {
      "id" : "some_id",
      "intervals" : [ "2013-05-13T00:00:00.000Z/2013-05-14T00:00:00.000Z" ],
      "columns" : {
        "__time" : {
          "type" : "LONG",
          "size" : 407240380,
          "cardinality" : null
        },
        "dim1" : {
          "type" : "STRING",
          "size" : 100000,
          "cardinality" : 1944
        },
        "dim2" : {
          "type" : "STRING",
          "size" : 100000,
          "cardinality" : 1504
        },
        "metric1" : {
          "type" : "FLOAT",
          "size" : 100000,
          "cardinality" : null
        }
      },
      "size" : 300000
    } ]
    </code>