如何在 clickhouse 中使用 groupBitmapAnd 和 AggregatingMergeTree 引擎？

Question

我想在 clickhouse 中维护一个表，它使用位图“AND”逻辑来合并具有相同 tag_id 行的位图。

由于位图在 clickhouse 中定义为 AggregateFunction(groupBitmap, UInt*) 并且 groupBitmapAnd 将位图作为其参数，因此我创建了一个如下表：

CREATE TABLE test.bitmap_column_expr_test2
(
    `tag_id` String,
    `z` AggregateFunction(groupBitmapAnd, AggregateFunction(groupBitmap, UInt32))
)
ENGINE = AggregatingMergeTree()
ORDER BY tag_id
SETTINGS index_granularity = 8192

就我而言，我想插入如下数据：

INSERT INTO test.bitmap_column_expr_test2 VALUES ('tag1', groupBitmapAndState(bitmapBuild(cast([1,2,3,4] as Array(UInt32)))));
INSERT INTO test.bitmap_column_expr_test2 VALUES ('tag1', groupBitmapAndState(bitmapBuild(cast([1] as Array(UInt32)))));
INSERT INTO test.bitmap_column_expr_test2 VALUES ('tag1', groupBitmapAndState(bitmapBuild(cast([1,3,4] as Array(UInt32)))));

我希望通过以下方式获得位图和结果：

SELECT bitmapToArray(groupBitmapAndMergeState(z)) FROM test.bitmap_column_expr_test2;

但是，我的 ddl 被 clickhouse 重写为：

CREATE TABLE test.bitmap_column_expr_test2
(
    `tag_id` String,
    `z` AggregateFunction(groupBitmap, AggregateFunction(groupBitmap, UInt32))
)
ENGINE = AggregatingMergeTree()
ORDER BY tag_id

丢失了列z的原始定义

此外，插入最终会出现异常：

DB::Exception: Aggregate function groupBitmapAndState(bitmapBuild(CAST([1, 2, 3, 4], 'Array(UInt32)'))) is found in wrong place in query: While processing groupBitmapAndState(bitmapBuild(CAST([1, 2, 3, 4], 'Array(UInt32)'))) (version 20.11.4.13 (official build))

我不确定在 AggregatingMergeTree 中通过“AND”逻辑合并的行中获取位图是否正确。

Answer 1

groupBitmapAnd 接受表示为 AggregateFunction(groupBitmap, UInt_) 类型的位图作为参数。

ClickHouse 不支持嵌套聚合类型（在本例中为 AggregateFunction(groupBitmapAnd, AggregateFunction(groupBitmap, UInt_))）。

所以它需要遵循官方文档中描述的模式 - https://clickhouse.tech/docs/en/sql-reference/aggregate-functions/reference/groupbitmapand/#groupbitmapand:

CREATE TABLE bitmap_column_expr_test2
(
    tag_id String,
    z AggregateFunction(groupBitmap, UInt32)
)
ENGINE = MergeTree
ORDER BY tag_id;

INSERT INTO bitmap_column_expr_test2 VALUES ('tag1', bitmapBuild(cast([1,2,3,4,5,6,7,8,9,10] as Array(UInt32))));
INSERT INTO bitmap_column_expr_test2 VALUES ('tag2', bitmapBuild(cast([6,7,8,9,10,11,12,13,14,15] as Array(UInt32))));
INSERT INTO bitmap_column_expr_test2 VALUES ('tag3', bitmapBuild(cast([2,4,6,8,10,12] as Array(UInt32))));

SELECT groupBitmapAnd(z) FROM bitmap_column_expr_test2 WHERE like(tag_id, 'tag%');
┌─groupBitmapAnd(z)─┐
│               3   │
└───────────────────┘