ClickHouse/src/Storages/StorageView.cpp

#include <Interpreters/InterpreterSelectQuery.h>
#include <Interpreters/InterpreterSelectWithUnionQuery.h>
#include <Interpreters/Context.h>

#include <Parsers/ASTCreateQuery.h>
#include <Parsers/ASTSubquery.h>
#include <Parsers/ASTTablesInSelectQuery.h>
#include <Parsers/ASTSelectWithUnionQuery.h>

#include <Storages/StorageView.h>
#include <Storages/StorageFactory.h>
#include <Storages/SelectQueryDescription.h>

#include <Common/typeid_cast.h>

#include <Processors/Pipe.h>
#include <Processors/Transforms/MaterializingTransform.h>
#include <Processors/QueryPlan/ExpressionStep.h>
#include <Processors/QueryPlan/SettingQuotaAndLimitsStep.h>
#include <Processors/QueryPlan/BuildQueryPipelineSettings.h>
#include <Processors/QueryPlan/Optimizations/QueryPlanOptimizationSettings.h>

namespace DB
{

namespace ErrorCodes
{
    extern const int INCORRECT_QUERY;
    extern const int LOGICAL_ERROR;
}

namespace
{

void addSettingsChanges(ASTPtr ast, const Settings & settings)
{
    auto * settings_ast = ast->as<ASTSetQuery>();
    if (!settings_ast)
        throw DB::Exception(DB::ErrorCodes::LOGICAL_ERROR, "ASTSetQuery expected");

    settings_ast->is_standalone = false;
    if (settings_ast->changes.tryGet("join_use_nulls") == nullptr)
        settings_ast->changes.emplace_back("join_use_nulls", Field(settings.join_use_nulls));
}

/// Save to AST settings from context that affects view behaviour.
void saveSettingsToAst(ASTSelectWithUnionQuery * select, const Settings & settings)
{
    /// Check SETTINGS section on the top level
    if (select->settings_ast)
    {
        addSettingsChanges(select->settings_ast, settings);
        return;
    }

    /// We cannot add SETTINGS on the top level because it will clash with section from inner SELECT
    /// and will got query: SELECT ... SETTINGS ... SETTINGS ...

    /// Process every select in ast and add SETTINGS section to each
    for (const auto & child : select->list_of_selects->children)
    {
        auto * child_select = child->as<ASTSelectQuery>();
        if (!child_select)
            continue;

        ASTPtr ast_set_query = child_select->settings();
        if (ast_set_query)
        {
            /// Modify existing SETTINGS section
            addSettingsChanges(ast_set_query, settings);
        }
        else
        {
            /// Add SETTINGS section to query
            ast_set_query = std::make_shared<ASTSetQuery>();
            addSettingsChanges(ast_set_query, settings);
            child_select->setExpression(ASTSelectQuery::Expression::SETTINGS, std::move(ast_set_query));
        }
    }
}

}

StorageView::StorageView(
    const StorageID & table_id_,
    const ASTCreateQuery & query,
    const ColumnsDescription & columns_,
    const String & comment,
    const Settings & settings)
    : IStorage(table_id_)
{
    StorageInMemoryMetadata storage_metadata;
    storage_metadata.setColumns(columns_);
    storage_metadata.setComment(comment);

    if (!query.select)
        throw Exception("SELECT query is not specified for " + getName(), ErrorCodes::INCORRECT_QUERY);

    saveSettingsToAst(query.select, settings);
    SelectQueryDescription description;

    description.inner_query = query.select->ptr();
    storage_metadata.setSelectQuery(description);
    setInMemoryMetadata(storage_metadata);
}


Pipe StorageView::read(
    const Names & column_names,
    const StorageMetadataPtr & metadata_snapshot,
    SelectQueryInfo & query_info,
    ContextPtr context,
    QueryProcessingStage::Enum processed_stage,
    const size_t max_block_size,
    const unsigned num_streams)
{
    QueryPlan plan;
    read(plan, column_names, metadata_snapshot, query_info, context, processed_stage, max_block_size, num_streams);
    return plan.convertToPipe(
        QueryPlanOptimizationSettings::fromContext(context),
        BuildQueryPipelineSettings::fromContext(context));
}

void StorageView::read(
        QueryPlan & query_plan,
        const Names & column_names,
        const StorageMetadataPtr & metadata_snapshot,
        SelectQueryInfo & query_info,
        ContextPtr context,
        QueryProcessingStage::Enum /*processed_stage*/,
        const size_t /*max_block_size*/,
        const unsigned /*num_streams*/)
{
    ASTPtr current_inner_query = metadata_snapshot->getSelectQuery().inner_query;

    if (query_info.view_query)
    {
        if (!query_info.view_query->as<ASTSelectWithUnionQuery>())
            throw Exception("Unexpected optimized VIEW query", ErrorCodes::LOGICAL_ERROR);
        current_inner_query = query_info.view_query->clone();
    }

    InterpreterSelectWithUnionQuery interpreter(current_inner_query, context, {}, column_names);
    interpreter.buildQueryPlan(query_plan);

    /// It's expected that the columns read from storage are not constant.
    /// Because method 'getSampleBlockForColumns' is used to obtain a structure of result in InterpreterSelectQuery.
    auto materializing_actions = std::make_shared<ActionsDAG>(query_plan.getCurrentDataStream().header.getColumnsWithTypeAndName());
    materializing_actions->addMaterializingOutputActions();

    auto materializing = std::make_unique<ExpressionStep>(query_plan.getCurrentDataStream(), std::move(materializing_actions));
    materializing->setStepDescription("Materialize constants after VIEW subquery");
    query_plan.addStep(std::move(materializing));

    /// And also convert to expected structure.
    auto header = metadata_snapshot->getSampleBlockForColumns(column_names, getVirtuals(), getStorageID());
    auto convert_actions_dag = ActionsDAG::makeConvertingActions(
            query_plan.getCurrentDataStream().header.getColumnsWithTypeAndName(),
            header.getColumnsWithTypeAndName(),
            ActionsDAG::MatchColumnsMode::Name);

    auto converting = std::make_unique<ExpressionStep>(query_plan.getCurrentDataStream(), convert_actions_dag);
    converting->setStepDescription("Convert VIEW subquery result to VIEW table structure");
    query_plan.addStep(std::move(converting));
}

static ASTTableExpression * getFirstTableExpression(ASTSelectQuery & select_query)
{
    if (!select_query.tables() || select_query.tables()->children.empty())
        throw Exception("Logical error: no table expression in view select AST", ErrorCodes::LOGICAL_ERROR);

    auto * select_element = select_query.tables()->children[0]->as<ASTTablesInSelectQueryElement>();

    if (!select_element->table_expression)
        throw Exception("Logical error: incorrect table expression", ErrorCodes::LOGICAL_ERROR);

    return select_element->table_expression->as<ASTTableExpression>();
}

void StorageView::replaceWithSubquery(ASTSelectQuery & outer_query, ASTPtr view_query, ASTPtr & view_name)
{
    ASTTableExpression * table_expression = getFirstTableExpression(outer_query);

    if (!table_expression->database_and_table_name)
    {
        // If it's a view table function, add a fake db.table name.
        if (table_expression->table_function && table_expression->table_function->as<ASTFunction>()->name == "view")
            table_expression->database_and_table_name = std::make_shared<ASTIdentifier>("__view");
        else
            throw Exception("Logical error: incorrect table expression", ErrorCodes::LOGICAL_ERROR);
    }

    DatabaseAndTableWithAlias db_table(table_expression->database_and_table_name);
    String alias = db_table.alias.empty() ? db_table.table : db_table.alias;

    view_name = table_expression->database_and_table_name;
    table_expression->database_and_table_name = {};
    table_expression->subquery = std::make_shared<ASTSubquery>();
    table_expression->subquery->children.push_back(view_query);
    table_expression->subquery->setAlias(alias);

    for (auto & child : table_expression->children)
        if (child.get() == view_name.get())
            child = view_query;
}

ASTPtr StorageView::restoreViewName(ASTSelectQuery & select_query, const ASTPtr & view_name)
{
    ASTTableExpression * table_expression = getFirstTableExpression(select_query);

    if (!table_expression->subquery)
        throw Exception("Logical error: incorrect table expression", ErrorCodes::LOGICAL_ERROR);

    ASTPtr subquery = table_expression->subquery;
    table_expression->subquery = {};
    table_expression->database_and_table_name = view_name;

    for (auto & child : table_expression->children)
        if (child.get() == subquery.get())
            child = view_name;
    return subquery->children[0];
}

void registerStorageView(StorageFactory & factory)
{
    factory.registerStorage("View", [](const StorageFactory::Arguments & args)
    {
        if (args.query.storage)
            throw Exception("Specifying ENGINE is not allowed for a View", ErrorCodes::INCORRECT_QUERY);

        return StorageView::create(args.table_id, args.query, args.columns, args.comment, args.getLocalContext()->getSettingsRef());
    });
}

}