ClickHouse SQL

arraySum(x -> x * x, b)

可传 lambda 函数，相当于

arraySum(
	arrayMap(x -> x * x, b)
)

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with 子句不仅能定义临时表，还能定义常量、函数：

WITH
    toFloat64('nan') AS nan,
    xs -> ... AS mean_value,
    (a, b) -> ... AS normalized_dot,
    x -> ... AS clip_corr,
    x -> ... AS finite_or_null,
    (last_px, first_px) -> ... AS endpoint_return,

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sumResample(start, stop, step)(value, key)

先按 (start, stop, step) 分桶，按 key 把 value 装桶里，执行聚合，这里是 sum，返回数组。配合 group by 使用。

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SELECT arraySlice([10, 20, 30, 40, 50], 2, 3);
-- [20, 30, 40]

从第二个开始取三个。注意 ClickHouse 数组下标从 1 开始计算索引