write first draft of offset clause

src/DataStreams/OffsetBlockInputStream.cpp

@@ -0,0 +1,50 @@
+#include <algorithm>
+
+#include <DataStreams/OffsetBlockInputStream.h>
+
+
+namespace DB
+{
+
+OffsetBlockInputStream::OffsetBlockInputStream(
+    const BlockInputStreamPtr & input, UInt64 offset_, bool always_read_till_end_,
+    bool use_limit_as_total_rows_approx, bool with_ties_, const SortDescription & description_)
+    : offset(offset_), always_read_till_end(always_read_till_end_), with_ties(with_ties_)
+    , description(description_)
+{
+    if (use_limit_as_total_rows_approx)
+    {
+        addTotalRowsApprox(static_cast<size_t>(limit));
+    }
+
+    children.push_back(input);
+}
+
+Block OffsetBlockInputStream::readImpl()
+{
+    Block res;
+    UInt64 rows = 0;
+
+    do
+    {
+        res = children.back()->read();
+        if (!res)
+            return res;
+        rows = res.rows();
+        pos += rows;
+    } while (pos <= offset);
+
+    SharedBlockPtr ptr = new detail::SharedBlock(std::move(res));
+
+    /// give away a piece of the block
+    UInt64 start = std::max(
+        static_cast<Int64>(0),
+        static_cast<Int64>(offset) - static_cast<Int64>(pos) + static_cast<Int64>(rows));
+
+    for (size_t i = 0; i < ptr->columns(); ++i)
+        ptr->safeGetByPosition(i).column = ptr->safeGetByPosition(i).column->cut(start, rows);
+
+    return *ptr;
+}
+
+}

src/DataStreams/OffsetBlockInputStream.h

@@ -0,0 +1,47 @@
+#pragma once
+
+#include <DataStreams/IBlockInputStream.h>
+#include <Common/SharedBlockRowRef.h>
+#include <Core/SortDescription.h>
+
+
+namespace DB
+{
+
+
+/** Implements the LIMIT relational operation.
+  */
+class OffsetBlockInputStream : public IBlockInputStream
+{
+public:
+    /** If always_read_till_end = false (by default), then after reading enough data,
+      *  returns an empty block, and this causes the query to be canceled.
+      * If always_read_till_end = true - reads all the data to the end, but ignores them. This is necessary in rare cases:
+      *  when otherwise, due to the cancellation of the request, we would not have received the data for GROUP BY WITH TOTALS from the remote server.
+      * If use_limit_as_total_rows_approx = true, then addTotalRowsApprox is called to use the limit in progress & stats
+      * with_ties = true, when query has WITH TIES modifier. If so, description should be provided
+      * description lets us know which row we should check for equality
+      */
+    OffsetBlockInputStream(
+            const BlockInputStreamPtr & input, UInt64 offset_,
+            bool always_read_till_end_ = false, bool use_limit_as_total_rows_approx = false,
+            bool with_ties_ = false, const SortDescription & description_ = {});
+
+    String getName() const override { return "Offset"; }
+
+    Block getHeader() const override { return children.at(0)->getHeader(); }
+
+protected:
+    Block readImpl() override;
+
+private:
+    UInt64 limit;
+    UInt64 offset;
+    UInt64 pos = 0;
+    bool always_read_till_end;
+    bool with_ties;
+    const SortDescription description;
+    SharedBlockRowRef ties_row_ref;
+};
+
+}

src/Interpreters/InterpreterSelectQuery.cpp

@@ -2,6 +2,7 @@
 #include <DataStreams/FilterBlockInputStream.h>
 #include <DataStreams/FinishSortingBlockInputStream.h>
 #include <DataStreams/LimitBlockInputStream.h>
+#include <DataStreams/OffsetBlockInputStream.h>
 #include <DataStreams/LimitByBlockInputStream.h>
 #include <DataStreams/PartialSortingBlockInputStream.h>
 #include <DataStreams/MergeSortingBlockInputStream.h>
@@ -92,6 +93,7 @@
 #include <Processors/Transforms/CubeTransform.h>
 #include <Processors/Transforms/FillingTransform.h>
 #include <Processors/LimitTransform.h>
+#include <Processors/OffsetTransform.h>
 #include <Processors/Transforms/FinishSortingTransform.h>
 #include <DataTypes/DataTypeAggregateFunction.h>
 #include <DataStreams/materializeBlock.h>
@@ -675,12 +677,9 @@ static std::pair<UInt64, UInt64> getLimitLengthAndOffset(const ASTSelectQuery &
     UInt64 offset = 0;
 
     if (query.limitLength())
-    {
         length = getLimitUIntValue(query.limitLength(), context);
-        if (query.limitOffset() && length)
-            offset = getLimitUIntValue(query.limitOffset(), context);
-    }
-
+    if (query.limitOffset())
+        offset = getLimitUIntValue(query.limitOffset(), context);
     return {length, offset};
 }
 
@@ -1065,6 +1064,8 @@ void InterpreterSelectQuery::executeImpl(TPipeline & pipeline, const BlockInputS
 
             if (!(pipeline_with_processors && has_prelimit))  /// Limit is no longer needed if there is prelimit.
                 executeLimit(pipeline);
+
+            executeOffset(pipeline);
         }
     }
 
@@ -2435,6 +2436,50 @@ void InterpreterSelectQuery::executeLimit(Pipeline & pipeline)
 }
 
 
+void InterpreterSelectQuery::executeOffset(Pipeline & pipeline)
+{
+    auto & query = getSelectQuery();
+    /// If there is LIMIT
+    if (!query.limitLength() && query.limitOffset())
+    {
+        /** Rare case:
+          *  if there is no WITH TOTALS and there is a subquery in FROM, and there is WITH TOTALS on one of the levels,
+          *  then when using LIMIT, you should read the data to the end, rather than cancel the query earlier,
+          *  because if you cancel the query, we will not get `totals` data from the remote server.
+          *
+          * Another case:
+          *  if there is WITH TOTALS and there is no ORDER BY, then read the data to the end,
+          *  otherwise TOTALS is counted according to incomplete data.
+          */
+        bool always_read_till_end = false;
+
+        if (query.group_by_with_totals && !query.orderBy())
+            always_read_till_end = true;
+
+        if (!query.group_by_with_totals && hasWithTotalsInAnySubqueryInFromClause(query))
+            always_read_till_end = true;
+
+        SortDescription order_descr;
+        if (query.limit_with_ties)
+        {
+            if (!query.orderBy())
+                throw Exception("LIMIT WITH TIES without ORDER BY", ErrorCodes::LOGICAL_ERROR);
+            order_descr = getSortDescription(query, *context);
+        }
+
+        UInt64 limit_length;
+        UInt64 limit_offset;
+        std::tie(limit_length, limit_offset) = getLimitLengthAndOffset(query, *context);
+
+        pipeline.transform([&](auto & stream)
+        {
+            std::cout << "BLOCK" << std::endl;
+            stream = std::make_shared<OffsetBlockInputStream>(stream, limit_offset, always_read_till_end, false, query.limit_with_ties, order_descr);
+        });
+    }
+}
+
+
 void InterpreterSelectQuery::executeWithFill(Pipeline & pipeline)
 {
     auto & query = getSelectQuery();
@@ -2529,6 +2574,54 @@ void InterpreterSelectQuery::executeLimit(QueryPipeline & pipeline)
 }
 
 
+void InterpreterSelectQuery::executeOffset(QueryPipeline & pipeline)
+{
+    auto & query = getSelectQuery();
+    /// If there is LIMIT
+    if (!query.limitLength() && query.limitOffset())
+    {
+        /** Rare case:
+          *  if there is no WITH TOTALS and there is a subquery in FROM, and there is WITH TOTALS on one of the levels,
+          *  then when using LIMIT, you should read the data to the end, rather than cancel the query earlier,
+          *  because if you cancel the query, we will not get `totals` data from the remote server.
+          *
+          * Another case:
+          *  if there is WITH TOTALS and there is no ORDER BY, then read the data to the end,
+          *  otherwise TOTALS is counted according to incomplete data.
+          */
+        bool always_read_till_end = false;
+
+        if (query.group_by_with_totals && !query.orderBy())
+            always_read_till_end = true;
+
+        if (!query.group_by_with_totals && hasWithTotalsInAnySubqueryInFromClause(query))
+            always_read_till_end = true;
+
+        UInt64 limit_length;
+        UInt64 limit_offset;
+        std::tie(limit_length, limit_offset) = getLimitLengthAndOffset(query, *context);
+
+        SortDescription order_descr;
+        if (query.limit_with_ties)
+        {
+            if (!query.orderBy())
+                throw Exception("LIMIT WITH TIES without ORDER BY", ErrorCodes::LOGICAL_ERROR);
+            order_descr = getSortDescription(query, *context);
+        }
+
+        pipeline.addSimpleTransform([&](const Block & header, QueryPipeline::StreamType stream_type) -> ProcessorPtr
+        {
+            if (stream_type != QueryPipeline::StreamType::Main)
+                return nullptr;
+            std::cout << "TRANSFORM" << std::endl;
+            return std::make_shared<OffsetTransform>(
+                    header, limit_length, limit_offset, 1, always_read_till_end, query.limit_with_ties, order_descr);
+        });
+    }
+}
+
+
+
 void InterpreterSelectQuery::executeExtremes(Pipeline & pipeline)
 {
     if (!context->getSettingsRef().extremes)

src/Interpreters/InterpreterSelectQuery.h

@@ -185,6 +185,7 @@ private:
     void executeUnion(Pipeline & pipeline, Block header);
     void executeLimitBy(Pipeline & pipeline);
     void executeLimit(Pipeline & pipeline);
+    void executeOffset(Pipeline & pipeline);
     static void executeProjection(Pipeline & pipeline, const ExpressionActionsPtr & expression);
     void executeDistinct(Pipeline & pipeline, bool before_order, Names columns);
     void executeExtremes(Pipeline & pipeline);
@@ -203,6 +204,7 @@ private:
     void executePreLimit(QueryPipeline & pipeline, bool do_not_skip_offset);
     void executeLimitBy(QueryPipeline & pipeline);
     void executeLimit(QueryPipeline & pipeline);
+    void executeOffset(QueryPipeline & pipeline);
     static void executeProjection(QueryPipeline & pipeline, const ExpressionActionsPtr & expression);
     void executeDistinct(QueryPipeline & pipeline, bool before_order, Names columns);
     void executeExtremes(QueryPipeline & pipeline);

src/Parsers/ParserSelectQuery.cpp

@@ -247,6 +247,11 @@ bool ParserSelectQuery::parseImpl(Pos & pos, ASTPtr & node, Expected & expected)
     {
         if (!exp_elem.parse(pos, limit_offset, expected))
             return false;
+        if (s_with_ties.ignore(pos, expected))
+        {
+            limit_with_ties_occured = true;
+            select_query->limit_with_ties = true;
+        }
     }
 
     /// Because TOP n in totally equals LIMIT n

src/Processors/OffsetTransform.cpp

@@ -0,0 +1,308 @@
+#include <Processors/OffsetTransform.h>
+
+
+namespace DB
+{
+
+namespace ErrorCodes
+{
+    extern const int LOGICAL_ERROR;
+}
+
+OffsetTransform::OffsetTransform(
+    const Block & header_, size_t limit_, size_t offset_, size_t num_streams,
+    bool always_read_till_end_, bool with_ties_,
+    SortDescription description_)
+    : IProcessor(InputPorts(num_streams, header_), OutputPorts(num_streams, header_))
+    , limit(limit_), offset(offset_)
+    , always_read_till_end(always_read_till_end_)
+    , with_ties(with_ties_), description(std::move(description_))
+{
+    if (num_streams != 1 && with_ties)
+        throw Exception("Cannot use OffsetTransform with multiple ports and ties.", ErrorCodes::LOGICAL_ERROR);
+
+    ports_data.resize(num_streams);
+
+    size_t cur_stream = 0;
+    for (auto & input : inputs)
+    {
+        ports_data[cur_stream].input_port = &input;
+        ++cur_stream;
+    }
+
+    cur_stream = 0;
+    for (auto & output : outputs)
+    {
+        ports_data[cur_stream].output_port = &output;
+        ++cur_stream;
+    }
+
+    for (const auto & desc : description)
+    {
+        if (!desc.column_name.empty())
+            sort_column_positions.push_back(header_.getPositionByName(desc.column_name));
+        else
+            sort_column_positions.push_back(desc.column_number);
+    }
+}
+
+Chunk OffsetTransform::makeChunkWithPreviousRow(const Chunk & chunk, size_t row) const
+{
+    assert(row < chunk.getNumRows());
+    ColumnRawPtrs current_columns = extractSortColumns(chunk.getColumns());
+    MutableColumns last_row_sort_columns;
+    for (size_t i = 0; i < current_columns.size(); ++i)
+    {
+        last_row_sort_columns.emplace_back(current_columns[i]->cloneEmpty());
+        last_row_sort_columns[i]->insertFrom(*current_columns[i], row);
+    }
+    return Chunk(std::move(last_row_sort_columns), 1);
+}
+
+
+IProcessor::Status OffsetTransform::prepare(
+        const PortNumbers & updated_input_ports,
+        const PortNumbers & updated_output_ports)
+{
+    bool has_full_port = false;
+
+    auto process_pair = [&](size_t pos)
+    {
+        auto status = preparePair(ports_data[pos]);
+
+        switch (status)
+        {
+            case IProcessor::Status::Finished:
+            {
+                if (!ports_data[pos].is_finished)
+                {
+                    ports_data[pos].is_finished = true;
+                    ++num_finished_port_pairs;
+                }
+
+                return;
+            }
+            case IProcessor::Status::PortFull:
+            {
+                has_full_port = true;
+                return;
+            }
+            case IProcessor::Status::NeedData:
+                return;
+            default:
+                throw Exception(
+                        "Unexpected status for OffsetTransform::preparePair : " + IProcessor::statusToName(status),
+                        ErrorCodes::LOGICAL_ERROR);
+
+        }
+    };
+
+    for (auto pos : updated_input_ports)
+        process_pair(pos);
+
+    for (auto pos : updated_output_ports)
+        process_pair(pos);
+
+    /// All ports are finished. It may happen even before we reached the limit (has less data then limit).
+    if (num_finished_port_pairs == ports_data.size())
+        return Status::Finished;
+
+    /// If we reached limit for some port, then close others. Otherwise some sources may infinitely read data.
+    /// Example: SELECT * FROM system.numbers_mt WHERE number = 1000000 LIMIT 1
+ //   if ((rows_read >= offset) && !previous_row_chunk && !always_read_till_end)
+   // {
+   //     for (auto & input : inputs)
+     //       input.close();
+
+      //  for (auto & output : outputs)
+        //    output.finish();
+
+        //return Status::Finished;
+    //}
+
+    if (has_full_port)
+        return Status::PortFull;
+
+    return Status::NeedData;
+}
+
+OffsetTransform::Status OffsetTransform::prepare()
+{
+    if (ports_data.size() != 1)
+        throw Exception("prepare without arguments is not supported for multi-port OffsetTransform.",
+                        ErrorCodes::LOGICAL_ERROR);
+
+    return prepare({0}, {0});
+}
+
+OffsetTransform::Status OffsetTransform::preparePair(PortsData & data)
+{
+    auto & output = *data.output_port;
+    auto & input = *data.input_port;
+
+    /// Check can output.
+    bool output_finished = false;
+    if (output.isFinished())
+    {
+        output_finished = true;
+        if (!always_read_till_end)
+        {
+            input.close();
+            return Status::Finished;
+        }
+    }
+
+    if (!output_finished && !output.canPush())
+    {
+        input.setNotNeeded();
+        return Status::PortFull;
+    }
+
+    /// Check can input.
+
+    if (input.isFinished())
+    {
+        output.finish();
+        return Status::Finished;
+    }
+
+    input.setNeeded();
+    if (!input.hasData())
+        return Status::NeedData;
+
+    data.current_chunk = input.pull(true);
+
+    auto rows = data.current_chunk.getNumRows();
+
+    if (rows_before_limit_at_least)
+        rows_before_limit_at_least->add(rows);
+
+    /// Skip block (for 'always_read_till_end' case).
+    if (output_finished)
+    {
+        data.current_chunk.clear();
+        if (input.isFinished())
+        {
+            output.finish();
+            return Status::Finished;
+        }
+
+        /// Now, we pulled from input, and it must be empty.
+        input.setNeeded();
+        return Status::NeedData;
+    }
+
+    /// Process block.
+
+    rows_read += rows;
+
+    //if (rows_read <= offset)
+    //{
+    //    data.current_chunk.clear();
+    //
+    //    if (input.isFinished())
+    //    {
+    //        output.finish();
+    //        return Status::Finished;
+    //    }
+
+        /// Now, we pulled from input, and it must be empty.
+    //    input.setNeeded();
+    //    return Status::NeedData;
+    //}
+
+    if (rows_read >= offset + rows && rows_read <= offset)
+    {
+        /// Return the whole chunk.
+
+        /// Save the last row of current chunk to check if next block begins with the same row (for WITH TIES).
+        if (with_ties && rows_read == offset + limit)
+            previous_row_chunk = makeChunkWithPreviousRow(data.current_chunk, data.current_chunk.getNumRows() - 1);
+    }
+    else
+        /// This function may be heavy to execute in prepare. But it happens no more then twice, and make code simpler.
+        splitChunk(data);
+
+    //bool may_need_more_data_for_ties = previous_row_chunk || rows_read - rows <= offset;
+    /// No more data is needed.
+    //if (!always_read_till_end && (rows_read >= offset) && !may_need_more_data_for_ties)
+    //    input.close();
+
+    output.push(std::move(data.current_chunk));
+
+    return Status::PortFull;
+}
+
+
+void OffsetTransform::splitChunk(PortsData & data)
+{
+    auto current_chunk_sort_columns = extractSortColumns(data.current_chunk.getColumns());
+    size_t num_rows = data.current_chunk.getNumRows();
+    size_t num_columns = data.current_chunk.getNumColumns();
+
+    /// return a piece of the block
+    size_t start = std::max(
+        static_cast<Int64>(0),
+        static_cast<Int64>(offset) - static_cast<Int64>(rows_read) + static_cast<Int64>(num_rows));
+
+    //size_t length = std::min(
+    //    static_cast<Int64>(rows_read) - static_cast<Int64>(offset),
+    //    static_cast<Int64>(offset) - static_cast<Int64>(rows_read) + static_cast<Int64>(num_rows));
+
+    size_t length = static_cast<Int64>(num_rows);
+    std::cout << "===========================" << std::endl
+              << start << " " << length << std::endl
+              << static_cast<Int64>(rows_read) << " " << static_cast<Int64>(num_rows) << std::endl
+              << "===========================" << std::endl;
+    /// check if other rows in current block equals to last one in limit
+    if (with_ties && length)
+    {
+        size_t current_row_num = start + length;
+        previous_row_chunk = makeChunkWithPreviousRow(data.current_chunk, current_row_num - 1);
+
+        for (; current_row_num < num_rows; ++current_row_num)
+        {
+            if (!sortColumnsEqualAt(current_chunk_sort_columns, current_row_num))
+            {
+                previous_row_chunk = {};
+                break;
+            }
+        }
+
+        length = current_row_num - start;
+    }
+
+    if (length == num_rows)
+        return;
+
+    auto columns = data.current_chunk.detachColumns();
+
+    for (size_t i = 0; i < num_columns; ++i)
+        columns[i] = columns[i]->cut(start, length);
+
+    data.current_chunk.setColumns(std::move(columns), length);
+}
+
+ColumnRawPtrs OffsetTransform::extractSortColumns(const Columns & columns) const
+{
+    ColumnRawPtrs res;
+    res.reserve(description.size());
+    for (size_t pos : sort_column_positions)
+        res.push_back(columns[pos].get());
+
+    return res;
+}
+
+bool OffsetTransform::sortColumnsEqualAt(const ColumnRawPtrs & current_chunk_sort_columns, size_t current_chunk_row_num) const
+{
+    assert(current_chunk_sort_columns.size() == previous_row_chunk.getNumColumns());
+    size_t size = current_chunk_sort_columns.size();
+    const auto & previous_row_sort_columns = previous_row_chunk.getColumns();
+    for (size_t i = 0; i < size; ++i)
+        if (0 != current_chunk_sort_columns[i]->compareAt(current_chunk_row_num, 0, *previous_row_sort_columns[i], 1))
+            return false;
+    return true;
+}
+
+}
+

src/Processors/OffsetTransform.h

@@ -0,0 +1,72 @@
+#pragma once
+
+#include <Processors/IProcessor.h>
+#include <Processors/RowsBeforeLimitCounter.h>
+#include <Core/SortDescription.h>
+
+namespace DB
+{
+
+/// Implementation for LIMIT N OFFSET M
+/// This processor support multiple inputs and outputs (the same number).
+/// Each pair of input and output port works independently.
+/// The reason to have multiple ports is to be able to stop all sources when limit is reached, in a query like:
+///     SELECT * FROM system.numbers_mt WHERE number = 1000000 LIMIT 1
+///
+/// always_read_till_end - read all data from input ports even if limit was reached.
+/// with_ties, description - implementation of LIMIT WITH TIES. It works only for single port.
+class OffsetTransform : public IProcessor
+{
+private:
+
+    size_t limit;
+    size_t offset;
+    bool always_read_till_end;
+
+    bool with_ties;
+    const SortDescription description;
+
+    Chunk previous_row_chunk;  /// for WITH TIES, contains only sort columns
+    std::vector<size_t> sort_column_positions;
+
+    size_t rows_read = 0; /// including the last read block
+    RowsBeforeLimitCounterPtr rows_before_limit_at_least;
+
+    /// State of port's pair.
+    /// Chunks from different port pairs are not mixed for berret cache locality.
+    struct PortsData
+    {
+        Chunk current_chunk;
+
+        InputPort * input_port = nullptr;
+        OutputPort * output_port = nullptr;
+        bool is_finished = false;
+    };
+
+    std::vector<PortsData> ports_data;
+    size_t num_finished_port_pairs = 0;
+
+    Chunk makeChunkWithPreviousRow(const Chunk & current_chunk, size_t row_num) const;
+    ColumnRawPtrs extractSortColumns(const Columns & columns) const;
+    bool sortColumnsEqualAt(const ColumnRawPtrs & current_chunk_sort_columns, size_t current_chunk_row_num) const;
+
+public:
+    OffsetTransform(
+        const Block & header_, size_t limit_, size_t offset_, size_t num_streams = 1,
+        bool always_read_till_end_ = false, bool with_ties_ = false,
+        SortDescription description_ = {});
+
+    String getName() const override { return "Limit"; }
+
+    Status prepare(const PortNumbers & /*updated_input_ports*/, const PortNumbers & /*updated_output_ports*/) override;
+    Status prepare() override; /// Compatibility for TreeExecutor.
+    Status preparePair(PortsData & data);
+    void splitChunk(PortsData & data);
+
+    InputPort & getInputPort() { return inputs.front(); }
+    OutputPort & getOutputPort() { return outputs.front(); }
+
+    void setRowsBeforeLimitCounter(RowsBeforeLimitCounterPtr counter) { rows_before_limit_at_least.swap(counter); }
+};
+
+}