SELECT
    floor((ReferrerTimestamp - InstallTimestamp) / 86400) AS DaysSinceInstallations
FROM 
(
    SELECT 6534090703218709881 AS DeviceIDHash, 1458586663 AS InstallTimestamp
    UNION ALL SELECT 2697418689476658272, 1458561552
) ANY INNER JOIN 
(
    SELECT 1034415739529768519 AS DeviceIDHash, 1458566664 AS ReferrerTimestamp
    UNION ALL SELECT 2697418689476658272, 1458561552
) USING DeviceIDHash;