x = np.random.normal(scale=50, size=100)
y = x + np.random.normal(scale=5, size=len(x))
df = pd.DataFrame({'x_val': x, 'y': y})

MosaicWidget(
    {
        "plot": [
            {
                "mark": "ruleX",
                "y1": {"agg": "avg(y) - stddev(y)/sqrt(count(y))"},
                "y2": {"agg": "avg(y) + stddev(y)/sqrt(count(y))"},
                "x": {"expr": "ntile(10) over (order by x_val)"},
                "marker": "tick",
                "data": {"from": "df"},
            }
        ]
    },
    data={'df': df},
)

> SELECT avg(y) - stddev(y)/sqrt(count(y)) AS "y1", avg(y) + stddev(y)/sqrt(count(y)) AS "y2", ntile(10) over (order by x_val) AS "x" FROM "df" AS "source" GROUP BY "x"
Binder Error: GROUP BY clause cannot contain window functions!

WITH "__mosaicTemp" AS (SELECT *, ntile(10) over (order by x_val) AS "x" FROM "df") SELECT avg(y) - stddev(y)/sqrt(count(y)) AS "y1", avg(y) + stddev(y)/sqrt(count(y)) AS "y2", "x" FROM "__mosaicTemp" GROUP BY "x"