如何在clickhouse中将groupBitmapAnd与AggregationMergeTree引擎一起使用

Question

我想在clickhouse中维护一个使用位图的表"与"；用于合并跨具有相同tag_id的行的位图的逻辑。

由于bitmap在clickhouse和groupBitmap中被定义为AggregateFunction(groupBitmap，UInt*(，并以bitmap为参数，我创建了一个表，如：

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

在我的情况下，我想插入以下数据：

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)))));

我希望通过获得位图And结果

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

然而，我的ddl被clickhouse改写为：

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

其失去了列CCD_ 1 的起源定义

此外，插入将以异常结束：

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))

我不确定我是否在做正确的事情来获得通过"合并的行的位图；"与"；AggregationingMergeTree中的逻辑。

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(在这种情况下，它是AggregateFunction(groupBitmapAnd，AggregateFunction(groupBitmap，UInt_(((。

因此，它需要遵循官方文件中描述的模式-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   │
└───────────────────┘