ClickHouse

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#include <Processors/QueryPlan/Optimizations/Optimizations.h>
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#include <Processors/QueryPlan/FilterStep.h>
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#include <Processors/QueryPlan/ExpressionStep.h>
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#include <Processors/QueryPlan/ArrayJoinStep.h>
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#include <Interpreters/ActionsDAG.h>
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#include <Interpreters/ArrayJoinAction.h>
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namespace DB::QueryPlanOptimizations
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{
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size_t tryLiftUpArrayJoin(QueryPlan::Node * parent_node, QueryPlan::Nodes & nodes)
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{
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    if (parent_node->children.size() != 1)
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        return 0;
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    QueryPlan::Node * child_node = parent_node->children.front();
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    auto & parent = parent_node->step;
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    auto & child = child_node->step;
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    auto * expression_step = typeid_cast<ExpressionStep *>(parent.get());
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    auto * filter_step = typeid_cast<FilterStep *>(parent.get());
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    auto * array_join_step = typeid_cast<ArrayJoinStep *>(child.get());
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    if (!(expression_step || filter_step) || !array_join_step)
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        return 0;
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    const auto & array_join = array_join_step->arrayJoin();
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    const auto & expression = expression_step ? expression_step->getExpression()
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                                              : filter_step->getExpression();
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    auto split_actions = expression->splitActionsBeforeArrayJoin(array_join->columns);
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    /// No actions can be moved before ARRAY JOIN.
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    if (split_actions.first->trivial())
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        return 0;
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    auto description = parent->getStepDescription();
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    /// Add new expression step before ARRAY JOIN.
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    /// Expression/Filter -> ArrayJoin -> Something
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    auto & node = nodes.emplace_back();
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    node.children.swap(child_node->children);
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    child_node->children.emplace_back(&node);
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    /// Expression/Filter -> ArrayJoin -> node -> Something
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    node.step = std::make_unique<ExpressionStep>(node.children.at(0)->step->getOutputStream(),
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                                                 std::move(split_actions.first));
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    node.step->setStepDescription(description);
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    array_join_step->updateInputStream(node.step->getOutputStream());
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    if (expression_step)
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        parent = std::make_unique<ExpressionStep>(array_join_step->getOutputStream(), split_actions.second);
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    else
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        parent = std::make_unique<FilterStep>(array_join_step->getOutputStream(), split_actions.second,
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                                              filter_step->getFilterColumnName(), filter_step->removesFilterColumn());
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    parent->setStepDescription(description + " [split]");
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    return 3;
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}
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}
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