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multiple join rewriter v2 (in progress)
This commit is contained in:
Artem Zuikov
parent
67d711e78c
commit
c45002a2ee
@ -34,12 +34,19 @@ namespace
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ASTPtr makeSubqueryTemplate()
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{
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ParserTablesInSelectQueryElement parser(true);
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ASTPtr subquery_template = parseQuery(parser, "(select * from _t)", 0);
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ASTPtr subquery_template = parseQuery(parser, "(select * from _t) as `--s`", 0);
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if (!subquery_template)
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throw Exception("Cannot parse subquery template", ErrorCodes::LOGICAL_ERROR);
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return subquery_template;
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}
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ASTPtr makeSubqueryQualifiedAsterisk()
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{
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auto asterisk = std::make_shared<ASTQualifiedAsterisk>();
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asterisk->children.emplace_back(std::make_shared<ASTIdentifier>("--s"));
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return asterisk;
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}
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/// Replace asterisks in select_expression_list with column identifiers
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class ExtractAsterisksMatcher
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{
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@ -50,6 +57,7 @@ public:
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std::vector<String> tables_order;
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std::shared_ptr<ASTExpressionList> new_select_expression_list;
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/// V1
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Data(const Context & context, const std::vector<const ASTTableExpression *> & table_expressions)
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{
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tables_order.reserve(table_expressions.size());
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@ -69,6 +77,19 @@ public:
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}
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}
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/// V2
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Data(const std::vector<TableWithColumnNamesAndTypes> & tables)
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{
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tables_order.reserve(tables.size());
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for (const auto & table : tables)
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{
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String table_name = table.table.getQualifiedNamePrefix(false);
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NamesAndTypesList columns = table.columns;
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tables_order.push_back(table_name);
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table_columns.emplace(std::move(table_name), std::move(columns));
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}
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}
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void addTableColumns(const String & table_name)
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{
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auto it = table_columns.find(table_name);
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@ -380,9 +401,10 @@ struct CollectColumnIdentifiersMatcher
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static bool needChildVisit(const ASTPtr & node, const ASTPtr &)
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{
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/// Do not go into subqueries. Do not collect table identifiers.
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/// Do not go into subqueries. Do not collect table identifiers. Do not get identifier from 't.*'.
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return !node->as<ASTSubquery>() &&
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!node->as<ASTTablesInSelectQuery>();
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!node->as<ASTTablesInSelectQuery>() &&
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!node->as<ASTQualifiedAsterisk>();
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}
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static void visit(const ASTPtr & ast, Data & data)
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@ -396,45 +418,45 @@ struct CollectColumnIdentifiersMatcher
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data.push_back(const_cast<ASTIdentifier *>(&ident));
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}
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};
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using CollectColumnIdentifiersVisitor = ConstInDepthNodeVisitor<CollectColumnIdentifiersMatcher, true>;
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struct TableNeededColumns
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struct CheckAliasDependencyVisitorData
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{
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const DatabaseAndTableWithAlias & table;
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NameSet no_clashes = {};
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NameSet column_clashes = {}; /// It's column for sure
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NameSet alias_clashes = {}; /// It's column or alias
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using TypeToVisit = ASTIdentifier;
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void fillExpressionList(ASTExpressionList & expression_list) const
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const Aliases & aliases;
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const ASTIdentifier * dependency = nullptr;
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void visit(ASTIdentifier & ident, ASTPtr &)
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{
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size_t columns_count = no_clashes.size() + column_clashes.size() + alias_clashes.size();
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expression_list.children.reserve(expression_list.children.size() + columns_count);
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String table_name = table.getQualifiedNamePrefix(false);
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for (auto & column : no_clashes)
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addShortName(column, expression_list);
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for (auto & column : column_clashes)
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addAliasedName(table_name, column, expression_list);
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for (auto & column : alias_clashes)
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addShortName(column, expression_list);
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}
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static void addShortName(const String & column, ASTExpressionList & expression_list)
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{
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auto ident = std::make_shared<ASTIdentifier>(column);
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expression_list.children.emplace_back(std::move(ident));
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}
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/// t.x as `t.x`
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static void addAliasedName(const String & table, const String & column, ASTExpressionList & expression_list)
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{
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auto ident = std::make_shared<ASTIdentifier>(std::vector<String>{table, column});
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ident->setAlias(table + '.' + column);
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expression_list.children.emplace_back(std::move(ident));
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if (!dependency && aliases.count(ident.name))
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dependency = &ident;
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}
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};
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using CheckAliasDependencyMatcher = OneTypeMatcher<CheckAliasDependencyVisitorData>;
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using CheckAliasDependencyVisitor = InDepthNodeVisitor<CheckAliasDependencyMatcher, true>;
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struct RewriteWithAliasMatcher
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{
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using Data = std::unordered_map<String, ASTPtr>;
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static bool needChildVisit(const ASTPtr & node, const ASTPtr &)
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{
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return !node->as<ASTSubquery>();
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}
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static void visit(ASTPtr & ast, Data & data)
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{
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String alias = ast->tryGetAlias();
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if (!alias.empty())
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{
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auto it = data.find(alias);
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if (it != data.end() && it->second.get() == ast.get())
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ast = std::make_shared<ASTIdentifier>(alias);
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}
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}
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};
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using RewriteWithAliasVisitor = InDepthNodeVisitor<RewriteWithAliasMatcher, true>;
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class SubqueryExpressionsRewriteMatcher
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{
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@ -442,9 +464,7 @@ public:
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struct Data
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{
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ASTPtr expression_list;
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const String & alias;
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bool rewritten = false;
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bool aliased = false;
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bool done = false;
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};
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static bool needChildVisit(ASTPtr & node, ASTPtr &)
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@ -456,28 +476,179 @@ public:
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{
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if (auto * t = ast->as<ASTSelectQuery>())
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visit(*t, ast, data);
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if (auto * t = ast->as<ASTSubquery>())
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visit(*t, ast, data);
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}
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private:
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static void visit(ASTSelectQuery & select, ASTPtr &, Data & data)
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{
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if (!data.rewritten)
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if (!data.done)
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select.setExpression(ASTSelectQuery::Expression::SELECT, std::move(data.expression_list));
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data.rewritten = true;
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data.done = true;
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}
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};
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using SubqueryExpressionsRewriteVisitor = InDepthNodeVisitor<SubqueryExpressionsRewriteMatcher, true>;
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struct TableNeededColumns
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{
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const DatabaseAndTableWithAlias & table;
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NameSet no_clashes = {};
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NameSet alias_clashes = {};
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std::unordered_map<String, String> column_clashes = {};
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void fillExpressionList(ASTExpressionList & expression_list) const
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{
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size_t columns_count = no_clashes.size() + column_clashes.size() + alias_clashes.size();
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expression_list.children.reserve(expression_list.children.size() + columns_count);
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String table_name = table.getQualifiedNamePrefix(false);
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for (auto & column : no_clashes)
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addShortName(column, expression_list);
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for (auto & column : alias_clashes)
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addShortName(column, expression_list);
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for (auto & [column, alias] : column_clashes)
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addAliasedName(table_name, column, alias, expression_list);
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}
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static void visit(ASTSubquery &, ASTPtr & ast, Data & data)
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static void addShortName(const String & column, ASTExpressionList & expression_list)
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{
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if (!data.aliased)
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ast->setAlias(data.alias);
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data.aliased = true;
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auto ident = std::make_shared<ASTIdentifier>(column);
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expression_list.children.emplace_back(std::move(ident));
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}
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/// t.x as `some`
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static void addAliasedName(const String & table, const String & column, const String & alias, ASTExpressionList & expression_list)
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{
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auto ident = std::make_shared<ASTIdentifier>(std::vector<String>{table, column});
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ident->setAlias(alias);
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expression_list.children.emplace_back(std::move(ident));
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}
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};
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using CollectColumnIdentifiersVisitor = ConstInDepthNodeVisitor<CollectColumnIdentifiersMatcher, true>;
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using SubqueryExpressionsRewriteVisitor = InDepthNodeVisitor<SubqueryExpressionsRewriteMatcher, true>;
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class UniqueShortNames
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{
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public:
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String get(const String & long_name)
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{
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auto it = names.find(long_name);
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if (it != names.end())
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return it->second;
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String unique_name = generateUniqueName();
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names.emplace(long_name, unique_name);
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return unique_name;
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}
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private:
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std::unordered_map<String, String> names;
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size_t counter = 0;
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String generateUniqueName()
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{
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static constexpr const char * pattern = "--x";
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return String(pattern) + std::to_string(counter++);
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}
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};
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size_t countSuchColumns(const std::vector<TableWithColumnNamesAndTypes> & tables, const String & short_name)
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{
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size_t count = 0;
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for (auto & table : tables)
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if (table.hasColumn(short_name))
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++count;
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return count;
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}
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/// Find clashes and normalize names
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/// 1. If column name has no clashes make all its occurrences short: 'table.column' -> 'column', 'table_alias.column' -> 'column'.
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/// 2. If column name can't be short cause of alias with same name generate and use unique name for it.
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/// 3. If column clashes with another column generate and use unique names for them.
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/// 4. If column clashes with another column and it's short - it's 'ambiguous column' error.
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/// 5. If column clashes with alias add short column name to select list. It would be removed later if not needed.
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std::vector<TableNeededColumns> normalizeColumnNamesExtractNeeded(
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const std::vector<TableWithColumnNamesAndTypes> & tables,
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const Aliases & aliases,
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std::vector<ASTIdentifier *> & identifiers)
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{
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UniqueShortNames unique_names;
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size_t last_table_pos = tables.size() - 1;
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std::vector<TableNeededColumns> needed_columns;
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needed_columns.reserve(tables.size());
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for (auto & table : tables)
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needed_columns.push_back(TableNeededColumns{table.table});
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for (ASTIdentifier * ident : identifiers)
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{
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bool got_alias = aliases.count(ident->name);
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if (auto table_pos = IdentifierSemantic::chooseTable(*ident, tables))
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{
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if (!ident->isShort())
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{
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if (got_alias)
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throw Exception("Alias clashes with qualified column '" + ident->name + "'", ErrorCodes::AMBIGUOUS_COLUMN_NAME);
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String short_name = ident->shortName();
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size_t count = countSuchColumns(tables, short_name);
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if (count > 1 || aliases.count(short_name))
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{
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auto & table = tables[*table_pos];
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IdentifierSemantic::setColumnLongName(*ident, table.table); /// table.column -> table_alias.column
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/// For tables moved into subselects we need unique short names for clashed names
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if (*table_pos != last_table_pos)
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{
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auto & unique_long_name = ident->name;
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String unique_short_name = unique_names.get(unique_long_name);
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ident->setShortName(unique_short_name);
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needed_columns[*table_pos].column_clashes.emplace(short_name, unique_short_name);
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}
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}
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else
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{
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ident->setShortName(short_name); /// table.column -> column
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needed_columns[*table_pos].no_clashes.emplace(std::move(short_name));
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}
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}
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else if (got_alias)
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needed_columns[*table_pos].alias_clashes.emplace(ident->shortName());
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else
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needed_columns[*table_pos].no_clashes.emplace(ident->shortName());
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}
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else if (!got_alias)
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throw Exception("Unknown column name '" + ident->name + "'", ErrorCodes::UNKNOWN_IDENTIFIER);
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}
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return needed_columns;
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}
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/// Make expression list for current subselect
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std::shared_ptr<ASTExpressionList> subqueryExpressionList(
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size_t table_pos,
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const std::vector<TableNeededColumns> & needed_columns,
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const std::vector<std::vector<ASTPtr>> & alias_pushdown)
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{
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auto expression_list = std::make_shared<ASTExpressionList>();
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/// First time extract needed left table columns manually.
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/// Next times extract left table columns via QualifiedAsterisk: `--s`.*
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if (table_pos == 1)
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needed_columns[0].fillExpressionList(*expression_list);
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else
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expression_list->children.emplace_back(makeSubqueryQualifiedAsterisk());
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/// Add needed right table columns
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needed_columns[table_pos].fillExpressionList(*expression_list);
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for (auto & expr : alias_pushdown[table_pos])
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expression_list->children.emplace_back(std::move(expr));
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return expression_list;
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}
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} /// namelesspace
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@ -493,121 +664,112 @@ void JoinToSubqueryTransformMatcher::visit(ASTPtr & ast, Data & data)
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}
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}
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/// The reason for V2: not to alias columns without clashes, use better `t.x` style aliases for others.
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/// The reason for V2: not to alias columns without clashes.
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/// It allows USING and 'select *' for queries with subselects. It doesn't need AsterisksSemantic and related stuff.
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/// 1. Expand asterisks in select expression list.
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/// 2. Normalize column names and find name clashes
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/// 3. Rewrite multiple JOINs with subqueries:
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/// SELECT ... FROM (SELECT `--join`.*, ... FROM (...) AS `--join` JOIN tableY ON ...) AS `--join` JOIN tableZ ON ...'
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/// 4. Push down expressions of aliases used in ON section into expression list of first reletad subquery
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void JoinToSubqueryTransformMatcher::visitV2(ASTSelectQuery & select, ASTPtr & ast, Data & data)
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{
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std::vector<const ASTTableExpression *> table_expressions;
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if (!needRewrite<2>(select, table_expressions))
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return;
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/// TODO: check table_expressions vs data.tables consistency
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auto & src_tables = select.tables()->children;
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size_t tables_count = src_tables.size();
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if (table_expressions.size() != data.tables.size() ||
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tables_count != data.tables.size())
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throw Exception("Inconsistent tables count in JOIN rewriter", ErrorCodes::LOGICAL_ERROR);
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/// Replace * and t.* with columns in select expression list.
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{
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ExtractAsterisksVisitor::Data asterisks_data(data.tables);
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ExtractAsterisksVisitor(asterisks_data).visit(select.select());
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if (asterisks_data.new_select_expression_list)
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select.setExpression(ASTSelectQuery::Expression::SELECT, std::move(asterisks_data.new_select_expression_list));
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}
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/// Collect column identifiers
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std::vector<ASTIdentifier *> identifiers;
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CollectColumnIdentifiersVisitor(identifiers).visit(ast);
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/// JOIN sections
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for (auto & child : select.tables()->children)
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std::vector<ASTIdentifier *> using_identifiers;
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std::vector<std::vector<ASTPtr>> alias_pushdown(tables_count);
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std::unordered_map<String, ASTPtr> on_aliases;
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/// Collect columns from JOIN sections. Detect if we have aliases there (they need pushdown).
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for (size_t table_pos = 0; table_pos < tables_count; ++table_pos)
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{
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auto * table = child->as<ASTTablesInSelectQueryElement>();
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auto * table = src_tables[table_pos]->as<ASTTablesInSelectQueryElement>();
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if (table->table_join)
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{
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auto & join = table->table_join->as<ASTTableJoin &>();
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if (join.on_expression)
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CollectColumnIdentifiersVisitor(identifiers).visit(join.on_expression);
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/// Nothing special for join.using_expression_list cause it contains short names
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}
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}
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/// Find clashes and normalize names:
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/// 1. If column name has no clashes make all its occurrences short: 'table.column' -> 'column', 'table_alias.column' -> 'column'.
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/// 2. If column name can't be short cause of same alias we keep it long converting 'table.column' -> 'table_alias.column' if any.
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/// 3. If column clashes with another column keep their names long but convert 'table.column' -> 'table_alias.column' if any.
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/// 4. If column clashes with another column and it's short - it's 'ambiguous column' error.
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/// 5. If column clashes with alias add short column name to select list. It would be removed later if not needed.
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/// @note Source query aliases should not clash with qualified names.
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std::vector<TableNeededColumns> needed_columns;
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needed_columns.reserve(data.tables.size());
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for (auto & table : data.tables)
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needed_columns.push_back(TableNeededColumns{table.table});
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NameSet alias_uses;
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for (ASTIdentifier * ident : identifiers)
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{
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bool got_alias = data.aliases.count(ident->name);
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if (auto table_pos = IdentifierSemantic::chooseTable(*ident, data.tables))
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{
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const String & short_name = ident->shortName();
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if (!ident->isShort())
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{
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if (got_alias)
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throw Exception("Alias clashes with qualified column '" + ident->name + "'", ErrorCodes::AMBIGUOUS_COLUMN_NAME);
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std::vector<ASTIdentifier *> on_identifiers;
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CollectColumnIdentifiersVisitor(on_identifiers).visit(join.on_expression);
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identifiers.insert(identifiers.end(), on_identifiers.begin(), on_identifiers.end());
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size_t count = 0;
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for (auto & table : data.tables)
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if (table.hasColumn(short_name))
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++count;
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if (count > 1 || data.aliases.count(short_name))
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/// Extract aliases used in ON section for pushdown. Exclude the last table.
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if (table_pos < tables_count - 1)
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{
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auto & table = data.tables[*table_pos];
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IdentifierSemantic::setColumnLongName(*ident, table.table); /// table.column -> table_alias.column
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needed_columns[*table_pos].column_clashes.emplace(short_name);
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}
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else
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{
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ident->setShortName(short_name); /// table.column -> column
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needed_columns[*table_pos].no_clashes.emplace(short_name);
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for (auto * ident : on_identifiers)
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{
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auto it = data.aliases.find(ident->name);
|
||||
if (!on_aliases.count(ident->name) && it != data.aliases.end())
|
||||
{
|
||||
auto alias_expression = it->second;
|
||||
alias_pushdown[table_pos].push_back(alias_expression);
|
||||
on_aliases[ident->name] = alias_expression;
|
||||
}
|
||||
}
|
||||
}
|
||||
}
|
||||
else if (got_alias)
|
||||
needed_columns[*table_pos].alias_clashes.emplace(short_name);
|
||||
else
|
||||
needed_columns[*table_pos].no_clashes.emplace(short_name);
|
||||
else if (join.using_expression_list)
|
||||
CollectColumnIdentifiersVisitor(using_identifiers).visit(join.on_expression);
|
||||
}
|
||||
else if (got_alias)
|
||||
alias_uses.insert(ident->name);
|
||||
else
|
||||
throw Exception("Unknown column name '" + ident->name + "'", ErrorCodes::UNKNOWN_IDENTIFIER);
|
||||
}
|
||||
|
||||
/// Rewrite tables
|
||||
/// Check if alias expression is too complex to push it down.
|
||||
for (auto & expr : on_aliases)
|
||||
{
|
||||
CheckAliasDependencyVisitor::Data check{data.aliases};
|
||||
CheckAliasDependencyVisitor(check).visit(expr.second);
|
||||
if (check.dependency)
|
||||
throw Exception("Cannot rewrite JOINs. Alias '" + expr.first +
|
||||
"' used in ON section depends on another alias '" + check.dependency->name + "'",
|
||||
ErrorCodes::NOT_IMPLEMENTED);
|
||||
}
|
||||
|
||||
/// Check same name in aliases, USING and ON sections. Cannot push down alias to ON through USING cause of name masquerading.
|
||||
for (auto * ident : using_identifiers)
|
||||
if (on_aliases.count(ident->name))
|
||||
throw Exception("Cannot rewrite JOINs. Alias '" + ident->name + "' appears both in ON and USING", ErrorCodes::NOT_IMPLEMENTED);
|
||||
using_identifiers.clear();
|
||||
|
||||
/// Replace pushdowned expressions with aliases names in original expression lists.
|
||||
RewriteWithAliasVisitor(on_aliases).visit(ast);
|
||||
on_aliases.clear();
|
||||
|
||||
std::vector<TableNeededColumns> needed_columns =
|
||||
normalizeColumnNamesExtractNeeded(data.tables, data.aliases, identifiers);
|
||||
|
||||
/// Rewrite JOINs with subselects
|
||||
|
||||
auto & src_tables = select.tables()->children;
|
||||
ASTPtr left_table = src_tables[0];
|
||||
|
||||
static ASTPtr subquery_template = makeSubqueryTemplate();
|
||||
static constexpr const char * join_subquery_alias = "--join";
|
||||
|
||||
for (size_t i = 1; i < src_tables.size() - 1; ++i)
|
||||
{
|
||||
String prev_join_alias = String(join_subquery_alias) + std::to_string(i-1);
|
||||
String current_join_alias = String(join_subquery_alias) + std::to_string(i);
|
||||
|
||||
auto expression_list = std::make_shared<ASTExpressionList>();
|
||||
{
|
||||
if (i == 1)
|
||||
{
|
||||
/// First time extract needed left table columns manually
|
||||
needed_columns[0].fillExpressionList(*expression_list);
|
||||
}
|
||||
else
|
||||
{
|
||||
/// Next times extract left tables via QualifiedAsterisk
|
||||
auto asterisk = std::make_shared<ASTQualifiedAsterisk>();
|
||||
asterisk->children.emplace_back(std::make_shared<ASTIdentifier>(prev_join_alias));
|
||||
expression_list->children.emplace_back(std::move(asterisk));
|
||||
}
|
||||
|
||||
/// Add needed right table columns
|
||||
needed_columns[i].fillExpressionList(*expression_list);
|
||||
}
|
||||
auto expression_list = subqueryExpressionList(i, needed_columns, alias_pushdown);
|
||||
|
||||
ASTPtr subquery = subquery_template->clone();
|
||||
SubqueryExpressionsRewriteVisitor::Data expr_rewrite_data{std::move(expression_list), current_join_alias};
|
||||
SubqueryExpressionsRewriteVisitor::Data expr_rewrite_data{std::move(expression_list)};
|
||||
SubqueryExpressionsRewriteVisitor(expr_rewrite_data).visit(subquery);
|
||||
|
||||
left_table = replaceJoin(left_table, src_tables[i], subquery);
|
||||
|
||||
Loading…
Reference in New Issue
Block a user