ClickHouse/src/Interpreters/JoinToSubqueryTransformVisitor.cpp

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#include <Common/typeid_cast.h>
#include <Core/NamesAndTypes.h>
#include <Interpreters/JoinToSubqueryTransformVisitor.h>
#include <Interpreters/IdentifierSemantic.h>
#include <Interpreters/AsteriskSemantic.h>
#include <Interpreters/DatabaseAndTableWithAlias.h>
#include <Parsers/ASTSelectQuery.h>
#include <Parsers/ASTSubquery.h>
#include <Parsers/ASTTablesInSelectQuery.h>
#include <Parsers/ASTIdentifier.h>
#include <Parsers/ASTExpressionList.h>
#include <Parsers/ASTFunction.h>
#include <Parsers/ParserTablesInSelectQuery.h>
#include <Parsers/ExpressionListParsers.h>
#include <Parsers/parseQuery.h>
#include <IO/WriteHelpers.h>
#include <Core/Defines.h>
namespace DB
{
namespace ErrorCodes
{
extern const int LOGICAL_ERROR;
extern const int AMBIGUOUS_COLUMN_NAME;
extern const int NOT_IMPLEMENTED;
extern const int UNKNOWN_IDENTIFIER;
}
namespace
{
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/// @note we use `--` prefix for unique short names and `--.` for subqueries.
/// It expects that user do not use names starting with `--` and column names starting with dot.
ASTPtr makeSubqueryTemplate()
{
ParserTablesInSelectQueryElement parser(true);
ASTPtr subquery_template = parseQuery(parser, "(select * from _t) as `--.s`", 0, DBMS_DEFAULT_MAX_PARSER_DEPTH);
if (!subquery_template)
throw Exception("Cannot parse subquery template", ErrorCodes::LOGICAL_ERROR);
return subquery_template;
}
ASTPtr makeSubqueryQualifiedAsterisk()
{
auto asterisk = std::make_shared<ASTQualifiedAsterisk>();
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asterisk->children.emplace_back(std::make_shared<ASTIdentifier>("--.s"));
return asterisk;
}
/// Replace asterisks in select_expression_list with column identifiers
class ExtractAsterisksMatcher
{
public:
struct Data
{
std::unordered_map<String, NamesAndTypesList> table_columns;
std::vector<String> tables_order;
std::shared_ptr<ASTExpressionList> new_select_expression_list;
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explicit Data(const std::vector<TableWithColumnNamesAndTypes> & tables)
{
tables_order.reserve(tables.size());
for (const auto & table : tables)
{
String table_name = table.table.getQualifiedNamePrefix(false);
NamesAndTypesList columns = table.columns;
tables_order.push_back(table_name);
table_columns.emplace(std::move(table_name), std::move(columns));
}
}
void addTableColumns(const String & table_name)
{
auto it = table_columns.find(table_name);
if (it == table_columns.end())
throw Exception("Unknown qualified identifier: " + table_name, ErrorCodes::UNKNOWN_IDENTIFIER);
for (const auto & column : it->second)
new_select_expression_list->children.push_back(
std::make_shared<ASTIdentifier>(std::vector<String>{it->first, column.name}));
}
};
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static bool needChildVisit(const ASTPtr &, const ASTPtr &) { return false; }
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static void visit(const ASTPtr & ast, Data & data)
{
if (auto * t = ast->as<ASTExpressionList>())
visit(*t, ast, data);
}
private:
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static void visit(const ASTExpressionList & node, const ASTPtr &, Data & data)
{
bool has_asterisks = false;
data.new_select_expression_list = std::make_shared<ASTExpressionList>();
data.new_select_expression_list->children.reserve(node.children.size());
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for (const auto & child : node.children)
{
if (child->as<ASTAsterisk>())
{
has_asterisks = true;
for (auto & table_name : data.tables_order)
data.addTableColumns(table_name);
}
else if (child->as<ASTQualifiedAsterisk>())
{
has_asterisks = true;
if (child->children.size() != 1)
throw Exception("Logical error: qualified asterisk must have exactly one child", ErrorCodes::LOGICAL_ERROR);
ASTIdentifier & identifier = child->children[0]->as<ASTIdentifier &>();
data.addTableColumns(identifier.name);
}
else
data.new_select_expression_list->children.push_back(child);
}
if (!has_asterisks)
data.new_select_expression_list.reset();
}
};
/// Find columns with aliases to push them into rewritten subselects.
/// Normalize table aliases: table_name.column_name -> table_alias.column_name
/// Make aliases maps (alias -> column_name, column_name -> alias)
struct ColumnAliasesMatcher
{
using Visitor = ConstInDepthNodeVisitor<ColumnAliasesMatcher, true>;
struct Data
{
const std::vector<DatabaseAndTableWithAlias> tables;
bool public_names;
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AsteriskSemantic::RevertedAliases rev_aliases; /// long_name -> aliases
std::unordered_map<String, String> aliases; /// alias -> long_name
std::vector<std::pair<ASTIdentifier *, bool>> compound_identifiers;
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std::set<String> allowed_long_names; /// original names allowed as aliases '--t.x as t.x' (select expressions only).
bool inside_function = false;
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explicit Data(const std::vector<DatabaseAndTableWithAlias> && tables_)
: tables(tables_)
, public_names(false)
{}
void replaceIdentifiersWithAliases()
{
String hide_prefix = "--"; /// @note restriction: user should not use alises like `--table.column`
for (auto & [identifier, is_public] : compound_identifiers)
{
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String long_name = identifier->name;
auto it = rev_aliases.find(long_name);
if (it == rev_aliases.end())
{
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bool last_table = false;
{
if (auto best_table_pos = IdentifierSemantic::chooseTable(*identifier, tables))
last_table = (*best_table_pos + 1 == tables.size());
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}
if (!last_table)
{
String alias = hide_prefix + long_name;
aliases[alias] = long_name;
rev_aliases[long_name].push_back(alias);
IdentifierSemantic::coverName(*identifier, alias);
if (is_public)
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{
identifier->setAlias(long_name);
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allowed_long_names.insert(long_name);
}
}
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else if (is_public)
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identifier->setAlias(long_name); /// prevent crop long to short name
}
else
{
if (it->second.empty())
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throw Exception("No alias for '" + long_name + "'", ErrorCodes::LOGICAL_ERROR);
if (is_public && allowed_long_names.count(long_name))
; /// leave original name unchanged for correct output
else
IdentifierSemantic::coverName(*identifier, it->second[0]);
}
}
}
};
static bool needChildVisit(const ASTPtr & node, const ASTPtr &)
{
/// Do not go into subqueries. Function visits children itself.
if (node->as<ASTSubquery>() ||
node->as<ASTFunction>())
return false;
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return !node->as<ASTQualifiedAsterisk>();
}
static void visit(const ASTPtr & ast, Data & data)
{
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if (auto * t = ast->as<ASTIdentifier>())
visit(*t, ast, data);
else if (auto * f = ast->as<ASTFunction>())
visit(*f, ast, data);
/// Do not allow asterisks but ignore them inside functions. I.e. allow 'count(*)'.
if (!data.inside_function && (ast->as<ASTAsterisk>() || ast->as<ASTQualifiedAsterisk>()))
throw Exception("Multiple JOIN do not support asterisks for complex queries yet", ErrorCodes::NOT_IMPLEMENTED);
}
static void visit(const ASTFunction &, const ASTPtr & ast, Data & data)
{
/// Grandchild case: Function -> (ExpressionList) -> Asterisk
data.inside_function = true;
Visitor visitor(data);
for (auto & child : ast->children)
visitor.visit(child);
data.inside_function = false;
}
static void visit(const ASTIdentifier & const_node, const ASTPtr &, Data & data)
{
ASTIdentifier & node = const_cast<ASTIdentifier &>(const_node); /// we know it's not const
if (node.isShort())
return;
bool last_table = false;
String long_name;
if (auto table_pos = IdentifierSemantic::chooseTable(node, data.tables))
{
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const auto & table = data.tables[*table_pos];
IdentifierSemantic::setColumnLongName(node, table); /// table_name.column_name -> table_alias.column_name
long_name = node.name;
if (&table == &data.tables.back())
last_table = true;
}
if (long_name.empty())
throw Exception("Cannot refer column '" + node.name + "' to table", ErrorCodes::AMBIGUOUS_COLUMN_NAME);
String alias = node.tryGetAlias();
if (!alias.empty())
{
data.aliases[alias] = long_name;
data.rev_aliases[long_name].push_back(alias);
if (!last_table)
{
IdentifierSemantic::coverName(node, alias);
node.setAlias("");
}
}
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else if (node.compound())
data.compound_identifiers.emplace_back(&node, data.public_names);
}
};
/// Attach additional semantic info to generated selects.
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struct AppendSemanticVisitorData
{
using TypeToVisit = ASTSelectQuery;
AsteriskSemantic::RevertedAliasesPtr rev_aliases = {};
bool done = false;
void visit(ASTSelectQuery & select, ASTPtr &)
{
if (done || !rev_aliases || !select.select())
return;
for (auto & child : select.select()->children)
{
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if (auto * node = child->as<ASTAsterisk>())
AsteriskSemantic::setAliases(*node, rev_aliases);
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if (auto * node = child->as<ASTQualifiedAsterisk>())
AsteriskSemantic::setAliases(*node, rev_aliases);
}
done = true;
}
};
/// Replaces table elements with pair.
struct RewriteTablesVisitorData
{
using TypeToVisit = ASTTablesInSelectQuery;
ASTPtr left;
ASTPtr right;
bool done = false;
/// @note Do not change ASTTablesInSelectQuery itself. No need to change select.tables.
void visit(ASTTablesInSelectQuery &, ASTPtr & ast)
{
if (done)
return;
std::vector<ASTPtr> new_tables{left, right};
ast->children.swap(new_tables);
done = true;
}
};
template <size_t version = 1>
bool needRewrite(ASTSelectQuery & select, std::vector<const ASTTableExpression *> & table_expressions)
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{
if (!select.tables())
return false;
const auto * tables = select.tables()->as<ASTTablesInSelectQuery>();
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if (!tables)
return false;
size_t num_tables = tables->children.size();
if (num_tables <= 2)
return false;
size_t num_array_join = 0;
size_t num_using = 0;
table_expressions.reserve(num_tables);
for (size_t i = 0; i < num_tables; ++i)
{
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const auto * table = tables->children[i]->as<ASTTablesInSelectQueryElement>();
if (!table)
throw Exception("Table expected", ErrorCodes::LOGICAL_ERROR);
if (table->table_expression)
if (const auto * expression = table->table_expression->as<ASTTableExpression>())
table_expressions.push_back(expression);
if (!i)
continue;
if (!table->table_join && !table->array_join)
throw Exception("Joined table expected", ErrorCodes::LOGICAL_ERROR);
if (table->array_join)
{
++num_array_join;
continue;
}
const auto & join = table->table_join->as<ASTTableJoin &>();
if (isComma(join.kind))
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throw Exception("COMMA to CROSS JOIN rewriter is not enabled or cannot rewrite query", ErrorCodes::NOT_IMPLEMENTED);
if (join.using_expression_list)
++num_using;
}
if (num_tables - num_array_join <= 2)
return false;
/// it's not trivial to support mix of JOIN ON & JOIN USING cause of short names
if (num_using && version <= 1)
throw Exception("Multiple JOIN does not support USING", ErrorCodes::NOT_IMPLEMENTED);
if (num_array_join)
throw Exception("Multiple JOIN does not support mix with ARRAY JOINs", ErrorCodes::NOT_IMPLEMENTED);
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return true;
}
using RewriteMatcher = OneTypeMatcher<RewriteTablesVisitorData>;
using RewriteVisitor = InDepthNodeVisitor<RewriteMatcher, true>;
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using ExtractAsterisksVisitor = ConstInDepthNodeVisitor<ExtractAsterisksMatcher, true>;
using ColumnAliasesVisitor = ColumnAliasesMatcher::Visitor;
using AppendSemanticMatcher = OneTypeMatcher<AppendSemanticVisitorData>;
using AppendSemanticVisitor = InDepthNodeVisitor<AppendSemanticMatcher, true>;
/// V2 specific visitors
struct CollectColumnIdentifiersMatcher
{
using Data = std::vector<ASTIdentifier *>;
static bool needChildVisit(const ASTPtr & node, const ASTPtr &)
{
/// Do not go into subqueries. Do not collect table identifiers. Do not get identifier from 't.*'.
return !node->as<ASTSubquery>() &&
!node->as<ASTTablesInSelectQuery>() &&
!node->as<ASTQualifiedAsterisk>();
}
static void visit(const ASTPtr & ast, Data & data)
{
if (auto * t = ast->as<ASTIdentifier>())
visit(*t, ast, data);
}
static void visit(const ASTIdentifier & ident, const ASTPtr &, Data & data)
{
data.push_back(const_cast<ASTIdentifier *>(&ident));
}
};
using CollectColumnIdentifiersVisitor = ConstInDepthNodeVisitor<CollectColumnIdentifiersMatcher, true>;
struct CheckAliasDependencyVisitorData
{
using TypeToVisit = ASTIdentifier;
const Aliases & aliases;
const ASTIdentifier * dependency = nullptr;
void visit(ASTIdentifier & ident, ASTPtr &)
{
if (!dependency && aliases.count(ident.name))
dependency = &ident;
}
};
using CheckAliasDependencyMatcher = OneTypeMatcher<CheckAliasDependencyVisitorData>;
using CheckAliasDependencyVisitor = InDepthNodeVisitor<CheckAliasDependencyMatcher, true>;
struct RewriteWithAliasMatcher
{
using Data = std::unordered_map<String, ASTPtr>;
static bool needChildVisit(const ASTPtr & node, const ASTPtr &)
{
return !node->as<ASTSubquery>();
}
static void visit(ASTPtr & ast, Data & data)
{
String alias = ast->tryGetAlias();
if (!alias.empty())
{
auto it = data.find(alias);
if (it != data.end() && it->second.get() == ast.get())
ast = std::make_shared<ASTIdentifier>(alias);
}
}
};
using RewriteWithAliasVisitor = InDepthNodeVisitor<RewriteWithAliasMatcher, true>;
class SubqueryExpressionsRewriteMatcher
{
public:
struct Data
{
ASTPtr expression_list;
bool done = false;
};
static bool needChildVisit(ASTPtr & node, ASTPtr &)
{
return !node->as<ASTSelectQuery>();
}
static void visit(ASTPtr & ast, Data & data)
{
if (auto * t = ast->as<ASTSelectQuery>())
visit(*t, ast, data);
}
private:
static void visit(ASTSelectQuery & select, ASTPtr &, Data & data)
{
if (!data.done)
select.setExpression(ASTSelectQuery::Expression::SELECT, std::move(data.expression_list));
data.done = true;
}
};
using SubqueryExpressionsRewriteVisitor = InDepthNodeVisitor<SubqueryExpressionsRewriteMatcher, true>;
struct TableNeededColumns
{
const DatabaseAndTableWithAlias & table;
NameSet no_clashes = {};
NameSet alias_clashes = {};
std::unordered_map<String, String> column_clashes = {};
void fillExpressionList(ASTExpressionList & expression_list) const
{
size_t columns_count = no_clashes.size() + column_clashes.size() + alias_clashes.size();
expression_list.children.reserve(expression_list.children.size() + columns_count);
String table_name = table.getQualifiedNamePrefix(false);
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for (const auto & column : no_clashes)
addShortName(column, expression_list);
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for (const auto & column : alias_clashes)
addShortName(column, expression_list);
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for (const auto & [column, alias] : column_clashes)
addAliasedName(table_name, column, alias, expression_list);
}
static void addShortName(const String & column, ASTExpressionList & expression_list)
{
auto ident = std::make_shared<ASTIdentifier>(column);
expression_list.children.emplace_back(std::move(ident));
}
/// t.x as `some`
static void addAliasedName(const String & table, const String & column, const String & alias, ASTExpressionList & expression_list)
{
auto ident = std::make_shared<ASTIdentifier>(std::vector<String>{table, column});
ident->setAlias(alias);
expression_list.children.emplace_back(std::move(ident));
}
};
class UniqueShortNames
{
public:
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/// We know that long names are unique (do not clashes with others).
/// So we could make unique names base on this knolage by adding some unused prefix.
static constexpr const char * pattern = "--";
String longToShort(const String & long_name)
{
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auto it = long_to_short.find(long_name);
if (it != long_to_short.end())
return it->second;
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String short_name = generateUniqueName(long_name);
long_to_short.emplace(long_name, short_name);
return short_name;
}
private:
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std::unordered_map<String, String> long_to_short;
static String generateUniqueName(const String & long_name)
{
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return String(pattern) + long_name;
}
};
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size_t countTablesWithColumn(const std::vector<TableWithColumnNamesAndTypes> & tables, const String & short_name)
{
size_t count = 0;
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for (const auto & table : tables)
if (table.hasColumn(short_name))
++count;
return count;
}
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/// 'select `--t.x`, `--t.x`, ...' -> 'select `--t.x` as `t.x`, `t.x`, ...'
void restoreName(ASTIdentifier & ident, const String & original_name, NameSet & restored_names)
{
if (!ident.tryGetAlias().empty())
return;
if (original_name.empty())
return;
if (!restored_names.count(original_name))
{
ident.setAlias(original_name);
restored_names.emplace(original_name);
}
else
ident.setShortName(original_name);
}
/// Find clashes and normalize names
/// 1. If column name has no clashes make all its occurrences short: 'table.column' -> 'column', 'table_alias.column' -> 'column'.
/// 2. If column name can't be short cause of alias with same name generate and use unique name for it.
/// 3. If column clashes with another column generate and use unique names for them.
/// 4. If column clashes with another column and it's short - it's 'ambiguous column' error.
/// 5. If column clashes with alias add short column name to select list. It would be removed later if not needed.
std::vector<TableNeededColumns> normalizeColumnNamesExtractNeeded(
const std::vector<TableWithColumnNamesAndTypes> & tables,
const Aliases & aliases,
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const std::vector<ASTIdentifier *> & identifiers,
const std::unordered_set<ASTIdentifier *> & public_identifiers,
UniqueShortNames & unique_names)
{
size_t last_table_pos = tables.size() - 1;
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NameSet restored_names;
std::vector<TableNeededColumns> needed_columns;
needed_columns.reserve(tables.size());
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for (const auto & table : tables)
needed_columns.push_back(TableNeededColumns{table.table});
for (ASTIdentifier * ident : identifiers)
{
bool got_alias = aliases.count(ident->name);
if (auto table_pos = IdentifierSemantic::chooseTable(*ident, tables))
{
if (!ident->isShort())
{
if (got_alias)
throw Exception("Alias clashes with qualified column '" + ident->name + "'", ErrorCodes::AMBIGUOUS_COLUMN_NAME);
String short_name = ident->shortName();
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String original_long_name;
if (public_identifiers.count(ident))
original_long_name = ident->name;
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size_t count = countTablesWithColumn(tables, short_name);
if (count > 1 || aliases.count(short_name))
{
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const auto & table = tables[*table_pos];
IdentifierSemantic::setColumnLongName(*ident, table.table); /// table.column -> table_alias.column
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auto & unique_long_name = ident->name;
/// For tables moved into subselects we need unique short names for clashed names
if (*table_pos != last_table_pos)
{
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String unique_short_name = unique_names.longToShort(unique_long_name);
ident->setShortName(unique_short_name);
needed_columns[*table_pos].column_clashes.emplace(short_name, unique_short_name);
}
}
else
{
ident->setShortName(short_name); /// table.column -> column
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needed_columns[*table_pos].no_clashes.emplace(short_name);
}
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restoreName(*ident, original_long_name, restored_names);
}
else if (got_alias)
needed_columns[*table_pos].alias_clashes.emplace(ident->shortName());
else
needed_columns[*table_pos].no_clashes.emplace(ident->shortName());
}
else if (!got_alias)
throw Exception("Unknown column name '" + ident->name + "'", ErrorCodes::UNKNOWN_IDENTIFIER);
}
return needed_columns;
}
/// Make expression list for current subselect
std::shared_ptr<ASTExpressionList> subqueryExpressionList(
size_t table_pos,
const std::vector<TableNeededColumns> & needed_columns,
const std::vector<std::vector<ASTPtr>> & alias_pushdown)
{
auto expression_list = std::make_shared<ASTExpressionList>();
/// First time extract needed left table columns manually.
/// Next times extract left table columns via QualifiedAsterisk: `--s`.*
if (table_pos == 1)
needed_columns[0].fillExpressionList(*expression_list);
else
expression_list->children.emplace_back(makeSubqueryQualifiedAsterisk());
/// Add needed right table columns
needed_columns[table_pos].fillExpressionList(*expression_list);
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for (const auto & expr : alias_pushdown[table_pos])
expression_list->children.emplace_back(std::move(expr));
return expression_list;
}
} /// namelesspace
bool JoinToSubqueryTransformMatcher::needChildVisit(ASTPtr & node, const ASTPtr &)
{
return !node->as<ASTSubquery>();
}
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void JoinToSubqueryTransformMatcher::visit(ASTPtr & ast, Data & data)
{
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if (auto * t = ast->as<ASTSelectQuery>())
{
if (data.version == 1)
visitV1(*t, ast, data);
else
visitV2(*t, ast, data);
}
}
/// The reason for V2: not to alias columns without clashes.
/// It allows USING and 'select *' for queries with subselects. It doesn't need AsterisksSemantic and related stuff.
/// 1. Expand asterisks in select expression list.
/// 2. Normalize column names and find name clashes
/// 3. Rewrite multiple JOINs with subqueries:
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/// SELECT ... FROM (SELECT `--.s`.*, ... FROM (...) AS `--.s` JOIN tableY ON ...) AS `--.s` JOIN tableZ ON ...'
/// 4. Push down expressions of aliases used in ON section into expression list of first reletad subquery
void JoinToSubqueryTransformMatcher::visitV2(ASTSelectQuery & select, ASTPtr & ast, Data & data)
{
std::vector<const ASTTableExpression *> table_expressions;
if (!needRewrite<2>(select, table_expressions))
return;
auto & src_tables = select.tables()->children;
size_t tables_count = src_tables.size();
if (table_expressions.size() != data.tables.size() ||
tables_count != data.tables.size())
throw Exception("Inconsistent tables count in JOIN rewriter", ErrorCodes::LOGICAL_ERROR);
/// Replace * and t.* with columns in select expression list.
{
ExtractAsterisksVisitor::Data asterisks_data(data.tables);
ExtractAsterisksVisitor(asterisks_data).visit(select.select());
if (asterisks_data.new_select_expression_list)
select.setExpression(ASTSelectQuery::Expression::SELECT, std::move(asterisks_data.new_select_expression_list));
}
/// Collect column identifiers
std::vector<ASTIdentifier *> identifiers;
CollectColumnIdentifiersVisitor(identifiers).visit(ast);
std::vector<ASTIdentifier *> using_identifiers;
std::vector<std::vector<ASTPtr>> alias_pushdown(tables_count);
std::unordered_map<String, ASTPtr> on_aliases;
/// Collect columns from JOIN sections. Detect if we have aliases there (they need pushdown).
for (size_t table_pos = 0; table_pos < tables_count; ++table_pos)
{
auto * table = src_tables[table_pos]->as<ASTTablesInSelectQueryElement>();
if (table->table_join)
{
auto & join = table->table_join->as<ASTTableJoin &>();
if (join.on_expression)
{
std::vector<ASTIdentifier *> on_identifiers;
CollectColumnIdentifiersVisitor(on_identifiers).visit(join.on_expression);
identifiers.insert(identifiers.end(), on_identifiers.begin(), on_identifiers.end());
/// Extract aliases used in ON section for pushdown. Exclude the last table.
if (table_pos < tables_count - 1)
{
for (auto * ident : on_identifiers)
{
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 (join.using_expression_list)
CollectColumnIdentifiersVisitor(using_identifiers).visit(join.on_expression);
}
}
/// 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();
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/// We need to know if identifier is public. If so we have too keep its output name.
std::unordered_set<ASTIdentifier *> public_identifiers;
for (auto & top_level_child : select.select()->children)
if (auto * ident = top_level_child->as<ASTIdentifier>())
public_identifiers.insert(ident);
UniqueShortNames unique_names;
std::vector<TableNeededColumns> needed_columns =
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normalizeColumnNamesExtractNeeded(data.tables, data.aliases, identifiers, public_identifiers, unique_names);
/// Rewrite JOINs with subselects
ASTPtr left_table = src_tables[0];
static ASTPtr subquery_template = makeSubqueryTemplate();
for (size_t i = 1; i < src_tables.size() - 1; ++i)
{
auto expression_list = subqueryExpressionList(i, needed_columns, alias_pushdown);
ASTPtr subquery = subquery_template->clone();
SubqueryExpressionsRewriteVisitor::Data expr_rewrite_data{std::move(expression_list)};
SubqueryExpressionsRewriteVisitor(expr_rewrite_data).visit(subquery);
left_table = replaceJoin(left_table, src_tables[i], subquery);
}
RewriteVisitor::Data visitor_data{left_table, src_tables.back()};
RewriteVisitor(visitor_data).visit(select.refTables());
data.done = true;
}
void JoinToSubqueryTransformMatcher::visitV1(ASTSelectQuery & select, ASTPtr &, Data & data)
{
using RevertedAliases = AsteriskSemantic::RevertedAliases;
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std::vector<const ASTTableExpression *> table_expressions;
if (!needRewrite(select, table_expressions))
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return;
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if (table_expressions.size() != data.tables.size())
throw Exception("Inconsistent tables count in JOIN rewriter", ErrorCodes::LOGICAL_ERROR);
bool has_subquery = false;
for (const auto & expr : table_expressions)
if (expr->subquery)
has_subquery = true;
if (!has_subquery)
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{
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ExtractAsterisksVisitor::Data asterisks_data(data.tables);
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ExtractAsterisksVisitor(asterisks_data).visit(select.select());
if (asterisks_data.new_select_expression_list)
select.setExpression(ASTSelectQuery::Expression::SELECT, std::move(asterisks_data.new_select_expression_list));
}
ColumnAliasesVisitor::Data aliases_data(getDatabaseAndTables(select, ""));
if (select.select())
{
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/// TODO: there's a bug here. We need to publish only top-level ASTIdentifiers but visitor extracts all.
aliases_data.public_names = true;
ColumnAliasesVisitor(aliases_data).visit(select.select());
aliases_data.public_names = false;
}
if (select.where())
ColumnAliasesVisitor(aliases_data).visit(select.where());
if (select.prewhere())
ColumnAliasesVisitor(aliases_data).visit(select.prewhere());
if (select.orderBy())
ColumnAliasesVisitor(aliases_data).visit(select.orderBy());
if (select.groupBy())
ColumnAliasesVisitor(aliases_data).visit(select.groupBy());
if (select.having())
ColumnAliasesVisitor(aliases_data).visit(select.having());
/// JOIN sections
for (auto & child : select.tables()->children)
{
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auto * table = child->as<ASTTablesInSelectQueryElement>();
if (table->table_join)
{
auto & join = table->table_join->as<ASTTableJoin &>();
if (join.on_expression)
ColumnAliasesVisitor(aliases_data).visit(join.on_expression);
}
}
aliases_data.replaceIdentifiersWithAliases();
auto rev_aliases = std::make_shared<RevertedAliases>();
rev_aliases->swap(aliases_data.rev_aliases);
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auto & src_tables = select.tables()->children;
ASTPtr left_table = src_tables[0];
static ASTPtr subquery_template = makeSubqueryTemplate();
for (size_t i = 1; i < src_tables.size() - 1; ++i)
{
left_table = replaceJoin(left_table, src_tables[i], subquery_template->clone());
if (!left_table)
throw Exception("Cannot replace tables with subselect", ErrorCodes::LOGICAL_ERROR);
/// attach data to generated asterisk
AppendSemanticVisitor::Data semantic_data{rev_aliases, false};
AppendSemanticVisitor(semantic_data).visit(left_table);
}
/// replace tables in select with generated two-table join
RewriteVisitor::Data visitor_data{left_table, src_tables.back()};
RewriteVisitor(visitor_data).visit(select.refTables());
data.done = true;
}
ASTPtr JoinToSubqueryTransformMatcher::replaceJoin(ASTPtr ast_left, ASTPtr ast_right, ASTPtr subquery_template)
{
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const auto * left = ast_left->as<ASTTablesInSelectQueryElement>();
const auto * right = ast_right->as<ASTTablesInSelectQueryElement>();
if (!left || !right)
throw Exception("Two TablesInSelectQueryElements expected", ErrorCodes::LOGICAL_ERROR);
if (!right->table_join)
throw Exception("Table join expected", ErrorCodes::LOGICAL_ERROR);
/// replace '_t' with pair of joined tables
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RewriteVisitor::Data visitor_data{ast_left, ast_right};
RewriteVisitor(visitor_data).visit(subquery_template);
return subquery_template;
}
}