druid/docs/content/querying/limitspec.md

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Sort groupBy Query Results

The limitSpec field provides the functionality to sort and limit the set of results from a groupBy query. If you group by a single dimension and are ordering by a single metric, we highly recommend using TopN Queries instead. The performance will be substantially better. Available options are:

DefaultLimitSpec

The default limit spec takes a limit and the list of columns to do an orderBy operation over. The grammar is:

{
    "type"    : "default",
    "limit"   : <integer_value>,
    "columns" : [list of OrderByColumnSpec],
}

OrderByColumnSpec

OrderByColumnSpecs indicate how to do order by operations. Each order-by condition can be a jsonString or a map of the following form:

{
    "dimension" : "<Any dimension or metric name>",
    "direction" : <"ascending"|"descending">
}

If only the dimension is provided (as a JSON string), the default order-by is ascending.