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ClickHouse 实现数组交并差计算

ClickHouse 实现数组交并差计算

计算数组交集

函数:arrayIntersect(arr1,arr2,...)
功能说明:计算 arr1,arr2等数组元素交集。
返回值:交集元素子数组。
SQL 实例:

SELECT
arrayIntersect([1, 2, 3], [4, 5, 6]) AS noIntersect,
arrayIntersect([1, 2, 3], [2, 3, 4, 5, 6]) AS hasIntersect
FORMAT Vertical

输出:
noIntersect: []
hasIntersect: [3,2]

计算数组并集

组合使用函数来实现arrayDistinct(arrayConcat(a, b))。
SQL 实例:

SELECT
[1, 2] AS a,
[2, 3] AS b,
arrayDistinct(arrayConcat(a, b)) AS res
FORMAT Vertical

输出:
a: [1,2]
b: [2,3]
res: [1,2,3]

计算数组差集

差集的实现要有一些技术含量了(感觉 ClickHouse 后面应该内置数组差集计算函数,实现类似arrayExcept() 函数),需要使用数组交集函数arrayIntersect() 结合高阶函数 arrayMap()和 arrayFilter()来组合实现。
SQL 实例:

SELECT
arrayIntersect([1, 2, 3], [4, 5, 6]) AS noIntersect,
arrayIntersect([1, 2, 3], [2, 3, 4, 5, 6]) AS hasIntersect
FORMAT Vertical
SELECT
[1, 2] AS a,
[2, 3] AS b,
arrayFilter(x -> (x IS NOT NULL), arrayMap(x -> multiIf(x NOT IN arrayIntersect(a, b), x, NULL), a)) AS res
FORMAT Vertical

输出:
a: [1,2]
b: [2,3]
res: [1]

使用 交(INTERSECT)、并(UNION)、差(EXCEPT)的SQL子句关键字 实现

另外, ClickHouse 中有集合交(INTERSECT)、并(UNION)、差(EXCEPT)的SQL子句关键字,可以实现数组的交并差运算。实例 SQL 如下。

交集SQL:

SELECT a.i
FROM
(
SELECT arrayJoin([1, 2]) AS i
) AS a
INTERSECT
SELECT b.i
FROM
(
SELECT arrayJoin([2, 3]) AS i
) AS b

输出:2

并集 SQL:

SET union_default_mode = 'ALL';
SELECT DISTINCT t.i
FROM
(
SELECT a.i
FROM
(
SELECT arrayJoin([1, 2]) AS i
) AS a
UNION
SELECT b.i
FROM
(
SELECT arrayJoin([2, 3]) AS i
) AS b
) AS t

输出:
1
2
3

差集 SQL:

SELECT a.i
FROM
(
SELECT arrayJoin([1, 2]) AS i
) AS a
EXCEPT
SELECT b.i
FROM
(
SELECT arrayJoin([2, 3]) AS i
) AS b

输出:1

上述[1,2]和[2,3]分别表示要求差集的数组

数据函数解释:
arrayIntersect表示多个数组求交集
arrayConcat表示连接多个数组为一个数组
arrayDistinct表示将多个数组元素去重组合为一个数组
arrayMap表示使用lambda函数转换
arrayFilter表示使用lambda函数过滤

参考资料:

​​https://clickhouse.tech/docs/zh/sql-reference/functions/higher-order-functions/​​


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