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add comments; count exact number of inserted rows [#METR-23881]

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This commit is contained in:
artpaul 2016-12-30 18:40:12 +05:00
parent 273e58f8d7
commit c74b8e2366
2 changed files with 21 additions and 8 deletions
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10
dbms/include/DB/DataStreams/LimitByBlockInputStream.h
View File

@ -9,6 +9,12 @@
namespace DB
{
/** Implements LIMIT BY clause witch can be used to obtain a "top N by subgroup".
*
* For example, if you have table T like this (Num: 1 1 3 3 3 4 4 5 7 7 7 7),
* the query SELECT Num FROM T LIMIT 2 BY Num
* will give you the following result: (Num: 1 1 3 3 4 4 5 7 7).
*/
class LimitByBlockInputStream : public IProfilingBlockInputStream
{
public:
@ -27,8 +33,8 @@ private:
private:
using MapHashed = HashMap<UInt128, UInt64, UInt128TrivialHash>;
Names columns_names;
size_t group_size;
const Names columns_names;
const size_t group_size;
MapHashed keys_counts;
};

19
dbms/src/DataStreams/LimitByBlockInputStream.cpp
View File

@ -19,6 +19,8 @@ String LimitByBlockInputStream::getID() const
Block LimitByBlockInputStream::readImpl()
{
/// Execute until end of stream or until
/// a block with some new records will be gotten.
while (true)
{
Block block = children[0]->read();
@ -28,7 +30,7 @@ Block LimitByBlockInputStream::readImpl()
const ConstColumnPlainPtrs column_ptrs(getKeyColumns(block));
const size_t rows = block.rows();
IColumn::Filter filter(rows);
bool inserted = false;
size_t inserted_count = 0;
for (size_t i = 0; i < rows; ++i)
{
@ -40,17 +42,22 @@ Block LimitByBlockInputStream::readImpl()
hash.get128(key.first, key.second);
const bool valid = (keys_counts[key]++ < group_size);
filter[i] = valid;
inserted |= valid;
if (keys_counts[key]++ < group_size)
{
inserted_count++;
filter[i] = 1;
}
else
filter[i] = 0;
}
if (!inserted)
/// Just go to the next block if there isn't any new records in the current one.
if (!inserted_count)
continue;
size_t all_columns = block.columns();
for (size_t i = 0; i < all_columns; ++i)
block.getByPosition(i).column = block.getByPosition(i).column->filter(filter, -1);
block.getByPosition(i).column = block.getByPosition(i).column->filter(filter, inserted_count);
return block;
}