ClickHouse/dbms/src/Interpreters/PredicateExpressionsOptimizer.cpp

#include <iostream>

#include <Common/typeid_cast.h>
#include <Storages/IStorage.h>
#include <Interpreters/PredicateExpressionsOptimizer.h>
#include <Interpreters/InterpreterSelectQuery.h>
#include <Interpreters/IdentifierSemantic.h>
#include <AggregateFunctions/AggregateFunctionFactory.h>
#include <Parsers/IAST.h>
#include <Parsers/ASTFunction.h>
#include <Parsers/ASTIdentifier.h>
#include <Parsers/ASTSelectQuery.h>
#include <Parsers/ASTSelectWithUnionQuery.h>
#include <Parsers/ASTSubquery.h>
#include <Parsers/ASTTablesInSelectQuery.h>
#include <Parsers/ASTAsterisk.h>
#include <Parsers/ASTQualifiedAsterisk.h>
#include <Parsers/queryToString.h>
#include <Interpreters/Context.h>
#include <Interpreters/ExpressionActions.h>
#include <Interpreters/QueryNormalizer.h>
#include <Interpreters/QueryAliasesVisitor.h>
#include "TranslateQualifiedNamesVisitor.h"

namespace DB
{

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

static constexpr auto and_function_name = "and";


struct FindIdentifierBestTableData
{
    using TypeToVisit = ASTIdentifier;

    const std::vector<DatabaseAndTableWithAlias> & tables;
    std::vector<std::pair<ASTIdentifier *, const DatabaseAndTableWithAlias *>> identifier_table;

    FindIdentifierBestTableData(const std::vector<DatabaseAndTableWithAlias> & tables_)
        : tables(tables_)
    {}

    void visit(ASTIdentifier & identifier, ASTPtr &)
    {
        const DatabaseAndTableWithAlias * best_table = nullptr;

        if (!identifier.compound())
        {
            if (!tables.empty())
                best_table = &tables[0];
        }
        else
        {
            size_t best_match = 0;
            for (const DatabaseAndTableWithAlias & table : tables)
            {
                if (size_t match = IdentifierSemantic::canReferColumnToTable(identifier, table))
                    if (match > best_match)
                    {
                        best_match = match;
                        best_table = &table;
                    }
            }
        }

        identifier_table.emplace_back(&identifier, best_table);
    }
};

using FindIdentifierBestTableMatcher = OneTypeMatcher<FindIdentifierBestTableData>;
using FindIdentifierBestTableVisitor = InDepthNodeVisitor<FindIdentifierBestTableMatcher, true>;


static bool allowPushDown(const ASTSelectQuery * subquery)
{
    return subquery &&
        !subquery->final() &&
        !subquery->limit_by_expression_list &&
        !subquery->limit_length &&
        !subquery->with_expression_list;
}


PredicateExpressionsOptimizer::PredicateExpressionsOptimizer(
    ASTSelectQuery * ast_select_, ExtractedSettings && settings_, const Context & context_)
        : ast_select(ast_select_), settings(settings_), context(context_)
{
}

bool PredicateExpressionsOptimizer::optimize()
{
    if (!settings.enable_optimize_predicate_expression || !ast_select || !ast_select->tables || ast_select->tables->children.empty())
        return false;

    if (!ast_select->where_expression && !ast_select->prewhere_expression)
        return false;

    SubqueriesProjectionColumns all_subquery_projection_columns = getAllSubqueryProjectionColumns();

    bool is_rewrite_subqueries = false;
    if (!all_subquery_projection_columns.empty())
    {
        is_rewrite_subqueries |= optimizeImpl(ast_select->where_expression, all_subquery_projection_columns, OptimizeKind::PUSH_TO_WHERE);
        is_rewrite_subqueries |= optimizeImpl(ast_select->prewhere_expression, all_subquery_projection_columns, OptimizeKind::PUSH_TO_PREWHERE);
    }
    return is_rewrite_subqueries;
}

bool PredicateExpressionsOptimizer::optimizeImpl(
    ASTPtr & outer_expression, SubqueriesProjectionColumns & subqueries_projection_columns, OptimizeKind expression_kind)
{
    /// split predicate with `and`
    std::vector<ASTPtr> outer_predicate_expressions = splitConjunctionPredicate(outer_expression);

    std::vector<DatabaseAndTableWithAlias> database_and_table_with_aliases =
        getDatabaseAndTables(*ast_select, context.getCurrentDatabase());

    bool is_rewrite_subquery = false;
    for (auto & outer_predicate : outer_predicate_expressions)
    {
        if (isArrayJoinFunction(outer_predicate))
            continue;

        auto outer_predicate_dependencies = getDependenciesAndQualifiers(outer_predicate, database_and_table_with_aliases);

        /// TODO: remove origin expression
        for (const auto & [subquery, projection_columns] : subqueries_projection_columns)
        {
            OptimizeKind optimize_kind = OptimizeKind::NONE;
            if (allowPushDown(subquery) && canPushDownOuterPredicate(projection_columns, outer_predicate_dependencies, optimize_kind))
            {
                if (optimize_kind == OptimizeKind::NONE)
                    optimize_kind = expression_kind;

                ASTPtr inner_predicate = outer_predicate->clone();
                cleanExpressionAlias(inner_predicate); /// clears the alias name contained in the outer predicate

                std::vector<IdentifierWithQualifier> inner_predicate_dependencies =
                    getDependenciesAndQualifiers(inner_predicate, database_and_table_with_aliases);

                setNewAliasesForInnerPredicate(projection_columns, inner_predicate_dependencies);

                switch (optimize_kind)
                {
                    case OptimizeKind::NONE: continue;
                    case OptimizeKind::PUSH_TO_WHERE: is_rewrite_subquery |= optimizeExpression(inner_predicate, subquery->where_expression, subquery); continue;
                    case OptimizeKind::PUSH_TO_HAVING: is_rewrite_subquery |= optimizeExpression(inner_predicate, subquery->having_expression, subquery); continue;
                    case OptimizeKind::PUSH_TO_PREWHERE: is_rewrite_subquery |= optimizeExpression(inner_predicate, subquery->prewhere_expression, subquery); continue;
                }
            }
        }
    }
    return is_rewrite_subquery;
}

std::vector<ASTPtr> PredicateExpressionsOptimizer::splitConjunctionPredicate(ASTPtr & predicate_expression)
{
    std::vector<ASTPtr> predicate_expressions;

    if (predicate_expression)
    {
        predicate_expressions.emplace_back(predicate_expression);

        auto remove_expression_at_index = [&predicate_expressions] (const size_t index)
        {
            if (index < predicate_expressions.size() - 1)
                std::swap(predicate_expressions[index], predicate_expressions.back());
            predicate_expressions.pop_back();
        };

        for (size_t idx = 0; idx < predicate_expressions.size();)
        {
            const auto expression = predicate_expressions.at(idx);

            if (const auto function = typeid_cast<ASTFunction *>(expression.get()))
            {
                if (function->name == and_function_name)
                {
                    for (auto & child : function->arguments->children)
                        predicate_expressions.emplace_back(child);

                    remove_expression_at_index(idx);
                    continue;
                }
            }
            idx++;
        }
    }
    return predicate_expressions;
}

std::vector<PredicateExpressionsOptimizer::IdentifierWithQualifier>
PredicateExpressionsOptimizer::getDependenciesAndQualifiers(ASTPtr & expression, std::vector<DatabaseAndTableWithAlias> & tables)
{
    FindIdentifierBestTableVisitor::Data find_data(tables);
    FindIdentifierBestTableVisitor(find_data).visit(expression);

    std::vector<IdentifierWithQualifier> dependencies;

    for (const auto & [identifier, table] : find_data.identifier_table)
    {
        String table_alias;
        if (table)
            table_alias = table->getQualifiedNamePrefix();

        dependencies.emplace_back(identifier, table_alias);
    }

    return dependencies;
}

static String qualifiedName(ASTIdentifier * identifier, const String & prefix)
{
    if (identifier->isShort())
        return prefix + identifier->getAliasOrColumnName();
    return identifier->getAliasOrColumnName();
}

bool PredicateExpressionsOptimizer::canPushDownOuterPredicate(
    const std::vector<ProjectionWithAlias> & projection_columns,
    const std::vector<IdentifierWithQualifier> & dependencies,
    OptimizeKind & optimize_kind)
{
    for (const auto & [identifier, prefix] : dependencies)
    {
        bool is_found = false;
        String qualified_name = qualifiedName(identifier, prefix);

        for (const auto & [ast, alias] : projection_columns)
        {
            if (alias == qualified_name)
            {
                is_found = true;
                if (isAggregateFunction(ast))
                    optimize_kind = OptimizeKind::PUSH_TO_HAVING;
            }
        }

        if (!is_found)
            return false;
    }

    return true;
}

void PredicateExpressionsOptimizer::setNewAliasesForInnerPredicate(
    const std::vector<ProjectionWithAlias> & projection_columns,
    const std::vector<IdentifierWithQualifier> & dependencies)
{
    for (auto & [identifier, prefix] : dependencies)
    {
        String qualified_name = qualifiedName(identifier, prefix);

        for (auto & [ast, alias] : projection_columns)
        {
            if (alias == qualified_name)
            {
                if (!isIdentifier(ast) && ast->tryGetAlias().empty())
                    ast->setAlias(ast->getColumnName());

                identifier->resetWithAlias(ast->getAliasOrColumnName());
            }
        }
    }
}

bool PredicateExpressionsOptimizer::isArrayJoinFunction(const ASTPtr & node)
{
    if (auto function = typeid_cast<ASTFunction *>(node.get()))
    {
        if (function->name == "arrayJoin")
            return true;
    }

    for (auto & child : node->children)
        if (isArrayJoinFunction(child))
            return true;

    return false;
}

bool PredicateExpressionsOptimizer::isAggregateFunction(const ASTPtr & node)
{
    if (auto function = typeid_cast<const ASTFunction *>(node.get()))
    {
        if (AggregateFunctionFactory::instance().isAggregateFunctionName(function->name))
            return true;
    }

    for (const auto & child : node->children)
        if (isAggregateFunction(child))
            return true;

    return false;
}

bool PredicateExpressionsOptimizer::optimizeExpression(const ASTPtr & outer_expression, ASTPtr & subquery_expression, ASTSelectQuery * subquery)
{
    ASTPtr new_subquery_expression = subquery_expression;
    new_subquery_expression = new_subquery_expression ? makeASTFunction(and_function_name, outer_expression, subquery_expression) : outer_expression;

    if (!subquery_expression)
        subquery->children.emplace_back(new_subquery_expression);
    else
        for (auto & child : subquery->children)
            if (child == subquery_expression)
                child = new_subquery_expression;

    subquery_expression = std::move(new_subquery_expression);
    return true;
}

PredicateExpressionsOptimizer::SubqueriesProjectionColumns PredicateExpressionsOptimizer::getAllSubqueryProjectionColumns()
{
    SubqueriesProjectionColumns projection_columns;

    for (const auto & table_expression : getSelectTablesExpression(*ast_select))
        if (table_expression->subquery)
            getSubqueryProjectionColumns(table_expression->subquery, projection_columns);

    return projection_columns;
}

void PredicateExpressionsOptimizer::getSubqueryProjectionColumns(const ASTPtr & subquery, SubqueriesProjectionColumns & projection_columns)
{
    String qualified_name_prefix = subquery->tryGetAlias();
    if (!qualified_name_prefix.empty())
        qualified_name_prefix += '.';

    const ASTPtr & subselect = subquery->children[0];

    ASTs select_with_union_projections;
    auto select_with_union_query = static_cast<ASTSelectWithUnionQuery *>(subselect.get());

    for (auto & select : select_with_union_query->list_of_selects->children)
    {
        std::vector<ProjectionWithAlias> subquery_projections;
        auto select_projection_columns = getSelectQueryProjectionColumns(select);

        if (!select_projection_columns.empty())
        {
            if (select_with_union_projections.empty())
                select_with_union_projections = select_projection_columns;

            for (size_t i = 0; i < select_projection_columns.size(); i++)
                subquery_projections.emplace_back(std::pair(select_projection_columns[i],
                                                            qualified_name_prefix + select_with_union_projections[i]->getAliasOrColumnName()));

            projection_columns.insert(std::pair(static_cast<ASTSelectQuery *>(select.get()), subquery_projections));
        }
    }
}

ASTs PredicateExpressionsOptimizer::getSelectQueryProjectionColumns(ASTPtr & ast)
{
    ASTs projection_columns;
    auto select_query = static_cast<ASTSelectQuery *>(ast.get());

    /// first should normalize query tree.
    std::unordered_map<String, ASTPtr> aliases;
    std::vector<DatabaseAndTableWithAlias> tables = getDatabaseAndTables(*select_query, context.getCurrentDatabase());

    TranslateQualifiedNamesVisitor::Data qn_visitor_data{{}, tables};
    TranslateQualifiedNamesVisitor(qn_visitor_data).visit(ast);

    QueryAliasesVisitor::Data query_aliases_data{aliases};
    QueryAliasesVisitor(query_aliases_data).visit(ast);

    QueryNormalizer::Data normalizer_data(aliases, settings);
    QueryNormalizer(normalizer_data).visit(ast);

    for (const auto & projection_column : select_query->select_expression_list->children)
    {
        if (typeid_cast<ASTAsterisk *>(projection_column.get()) || typeid_cast<ASTQualifiedAsterisk *>(projection_column.get()))
        {
            ASTs evaluated_columns = evaluateAsterisk(select_query, projection_column);

            for (const auto & column : evaluated_columns)
                projection_columns.emplace_back(column);

            continue;
        }

        projection_columns.emplace_back(projection_column);
    }
    return projection_columns;
}

ASTs PredicateExpressionsOptimizer::evaluateAsterisk(ASTSelectQuery * select_query, const ASTPtr & asterisk)
{
    /// SELECT *, SELECT dummy, SELECT 1 AS id
    if (!select_query->tables || select_query->tables->children.empty())
        return {};

    std::vector<const ASTTableExpression *> tables_expression = getSelectTablesExpression(*select_query);

    if (const auto qualified_asterisk = typeid_cast<ASTQualifiedAsterisk *>(asterisk.get()))
    {
        if (qualified_asterisk->children.size() != 1)
            throw Exception("Logical error: qualified asterisk must have exactly one child", ErrorCodes::LOGICAL_ERROR);

        DatabaseAndTableWithAlias ident_db_and_name(qualified_asterisk->children[0]);

        for (auto it = tables_expression.begin(); it != tables_expression.end();)
        {
            const ASTTableExpression * table_expression = *it;
            DatabaseAndTableWithAlias database_and_table_with_alias(*table_expression, context.getCurrentDatabase());

            if (ident_db_and_name.satisfies(database_and_table_with_alias, true))
                ++it;
            else
                it = tables_expression.erase(it); /// It's not a required table
        }
    }

    ASTs projection_columns;
    for (auto & table_expression : tables_expression)
    {
        if (table_expression->subquery)
        {
            const auto subquery = static_cast<const ASTSubquery *>(table_expression->subquery.get());
            const auto select_with_union_query = static_cast<ASTSelectWithUnionQuery *>(subquery->children[0].get());
            const auto subquery_projections = getSelectQueryProjectionColumns(select_with_union_query->list_of_selects->children[0]);
            projection_columns.insert(projection_columns.end(), subquery_projections.begin(), subquery_projections.end());
        }
        else
        {
            StoragePtr storage;

            if (table_expression->table_function)
            {
                auto query_context = const_cast<Context *>(&context.getQueryContext());
                storage = query_context->executeTableFunction(table_expression->table_function);
            }
            else if (table_expression->database_and_table_name)
            {
                const auto database_and_table_ast = static_cast<ASTIdentifier*>(table_expression->database_and_table_name.get());
                DatabaseAndTableWithAlias database_and_table_name(*database_and_table_ast);
                storage = context.getTable(database_and_table_name.database, database_and_table_name.table);
            }
            else
                throw Exception("Logical error: unexpected table expression", ErrorCodes::LOGICAL_ERROR);

            const auto block = storage->getSampleBlock();
            for (size_t idx = 0; idx < block.columns(); idx++)
                projection_columns.emplace_back(std::make_shared<ASTIdentifier>(block.getByPosition(idx).name));
        }
    }
    return projection_columns;
}

void PredicateExpressionsOptimizer::cleanExpressionAlias(ASTPtr & expression)
{
    const auto my_alias = expression->tryGetAlias();
    if (!my_alias.empty())
        expression->setAlias("");

    for (auto & child : expression->children)
        cleanExpressionAlias(child);
}

}