1 | #include <Processors/Transforms/LimitByTransform.h> |
2 | #include <Common/PODArray.h> |
3 | #include <Common/SipHash.h> |
4 | |
5 | namespace DB |
6 | { |
7 | |
8 | LimitByTransform::LimitByTransform(const Block & , size_t group_length_, size_t group_offset_, const Names & columns) |
9 | : ISimpleTransform(header, header, true) |
10 | , group_length(group_length_) |
11 | , group_offset(group_offset_) |
12 | { |
13 | key_positions.reserve(columns.size()); |
14 | |
15 | for (const auto & name : columns) |
16 | { |
17 | auto position = header.getPositionByName(name); |
18 | auto & column = header.getByPosition(position).column; |
19 | |
20 | /// Ignore all constant columns. |
21 | if (!(column && isColumnConst(*column))) |
22 | key_positions.emplace_back(position); |
23 | } |
24 | } |
25 | |
26 | void LimitByTransform::transform(Chunk & chunk) |
27 | { |
28 | size_t num_rows = chunk.getNumRows(); |
29 | auto columns = chunk.detachColumns(); |
30 | |
31 | IColumn::Filter filter(num_rows); |
32 | size_t inserted_count = 0; |
33 | |
34 | for (size_t row = 0; row < num_rows; ++row) |
35 | { |
36 | UInt128 key(0, 0); |
37 | SipHash hash; |
38 | |
39 | for (auto position : key_positions) |
40 | columns[position]->updateHashWithValue(row, hash); |
41 | |
42 | hash.get128(key.low, key.high); |
43 | |
44 | auto count = keys_counts[key]++; |
45 | if (count >= group_offset && count < group_length + group_offset) |
46 | { |
47 | inserted_count++; |
48 | filter[row] = 1; |
49 | } |
50 | else |
51 | filter[row] = 0; |
52 | } |
53 | |
54 | /// Just go to the next block if there isn't any new records in the current one. |
55 | if (!inserted_count) |
56 | /// SimpleTransform will skip it. |
57 | return; |
58 | |
59 | if (inserted_count < num_rows) |
60 | { |
61 | for (auto & column : columns) |
62 | if (isColumnConst(*column)) |
63 | column = column->cut(0, inserted_count); |
64 | else |
65 | column = column->filter(filter, inserted_count); |
66 | } |
67 | |
68 | chunk.setColumns(std::move(columns), inserted_count); |
69 | } |
70 | |
71 | } |
72 | |