datastore/tests/performance/limit_by_misc.xml

<test>
    <substitutions>
        <substitution>
            <name>cardinality</name>
            <values>
                <value>1000</value>
                <value>100000</value>
            </values>
        </substitution>
    </substitutions>

    <!-- Top-K: ORDER BY user ASC, ts DESC LIMIT N BY user -->
    <query>
        SELECT number % {cardinality} AS user, number AS ts
        FROM numbers_mt(10000000)
        ORDER BY user ASC, ts DESC LIMIT 10 BY user
        FORMAT NULL
    </query>

    <!-- Timestamp bucketing: LIMIT N BY toStartOfHour(ts), user_id -->
    <query>
        SELECT toStartOfHour(toDateTime(number % 86400)) AS hr,
               number % {cardinality} AS user, number AS v
        FROM numbers_mt(10000000)
        LIMIT 10 BY hr, user
        FORMAT NULL
    </query>

    <!-- Nullable BY key with ~10% nulls. -->
    <query>
        SELECT if(number % 10 = 0, NULL, number % {cardinality}) AS k, number AS v
        FROM numbers_mt(10000000)
        LIMIT 10 BY k
        FORMAT NULL
    </query>

    <!-- Very low cardinality: 4 groups -->
    <query>
        SELECT number % 4 AS k, number AS v
        FROM numbers_mt(10000000)
        ORDER BY v LIMIT 10 BY k
        FORMAT NULL
    </query>
</test>