SPY at-the-money implied volatility against realized volatility, by month

WITH
    monthly_iv AS
    (
        SELECT
            toStartOfMonth(date)                    AS m,
            round(avg(implied_volatility) * 100, 1) AS implied_vol_pct
        FROM global_markets.options_greeks
        WHERE underlying_symbol = 'SPY'
          AND iv_converged = 1
          AND volume > 0
          AND underlying_close > 0
          AND days_to_expiry BETWEEN 20 AND 45
          AND abs(toFloat64(strike_price) / toFloat64(underlying_close) - 1) < 0.05
          AND date >= '2025-08-01'
          AND date <  '2026-08-01'
        GROUP BY m
    ),
    monthly_rv AS
    (
        SELECT
            m,
            round(arrayReduce('stddevPop', rets) * sqrt(252) * 100, 1) AS realized_vol_pct
        FROM
        (
            SELECT
                m,
                arrayMap((a, b) -> log(a / b),
                         arraySlice(px, 2),
                         arraySlice(px, 1, length(px) - 1)) AS rets
            FROM
            (
                SELECT
                    toStartOfMonth(session_date) AS m,
                    arrayMap(t -> t.2, arraySort(t -> t.1, groupArray((session_date, session_close)))) AS px
                FROM
                (
                    SELECT
                        date                  AS session_date,
                        toFloat64(max(close)) AS session_close
                    FROM global_markets.stocks_daily_aggs
                    WHERE ticker = 'SPY'
                      AND date >= '2025-08-01'
                      AND date <  '2026-08-01'
                    GROUP BY date
                )
                GROUP BY m
            )
            WHERE length(rets) > 5
        )
    )
SELECT
    toString(iv.m)      AS month,
    iv.implied_vol_pct  AS implied_vol_pct,
    rv.realized_vol_pct AS realized_vol_pct
FROM monthly_iv AS iv
INNER JOIN monthly_rv AS rv ON rv.m = iv.m
ORDER BY iv.m