ClickHouse/tests/performance/window_functions.xml

<test>
    <preconditions>
        <table_exists>hits_100m_single</table_exists>
    </preconditions>

    <!--
        For some counters, find top 10 users by the numer of records.
        First with LIMIT BY, next with window functions.
    -->
    <query><![CDATA[
        select CounterID, UserID, count(*) c
        from hits_100m_single
        where CounterID < 10000
        group by CounterID, UserID
        order by c desc
        limit 10 by CounterID
        format Null
    ]]></query>

    <query><![CDATA[
        select *
        from (
            select *,
                count() over (partition by CounterID order by c desc) rank
                from (
                    select CounterID, UserID, count() c
                    from hits_100m_single
                    where CounterID < 10000
                    group by CounterID, UserID
                )
        )
        where rank <= 10
        format Null
    ]]></query>

</test>