ClickHouse/src/Interpreters/CrossToInnerJoinVisitor.cpp
2022-07-29 18:35:05 +02:00

278 lines
9.2 KiB
C++

#include <Common/typeid_cast.h>
#include <Parsers/queryToString.h>
#include <Functions/FunctionsComparison.h>
#include <Functions/FunctionsLogical.h>
#include <IO/WriteHelpers.h>
#include <Interpreters/CrossToInnerJoinVisitor.h>
#include <Interpreters/DatabaseAndTableWithAlias.h>
#include <Interpreters/IdentifierSemantic.h>
#include <Interpreters/misc.h>
#include <Parsers/ASTExpressionList.h>
#include <Parsers/ASTFunction.h>
#include <Parsers/ASTIdentifier.h>
#include <Parsers/ASTLiteral.h>
#include <Parsers/ASTSelectQuery.h>
#include <Parsers/ASTSubquery.h>
#include <Parsers/ASTTablesInSelectQuery.h>
#include <Parsers/ExpressionListParsers.h>
#include <Parsers/ParserTablesInSelectQuery.h>
#include <Parsers/parseQuery.h>
#include <Common/logger_useful.h>
namespace DB
{
namespace ErrorCodes
{
extern const int INCORRECT_QUERY;
extern const int LOGICAL_ERROR;
extern const int NOT_IMPLEMENTED;
}
namespace
{
struct JoinedElement
{
explicit JoinedElement(const ASTTablesInSelectQueryElement & table_element)
: element(table_element)
{
if (element.table_join)
{
join = element.table_join->as<ASTTableJoin>();
original_kind = join->kind;
}
}
void checkTableName(const DatabaseAndTableWithAlias & table, const String & current_database) const
{
if (!element.table_expression)
throw Exception("Not a table expression in JOIN (ARRAY JOIN?)", ErrorCodes::LOGICAL_ERROR);
ASTTableExpression * table_expression = element.table_expression->as<ASTTableExpression>();
if (!table_expression)
throw Exception("Wrong table expression in JOIN", ErrorCodes::LOGICAL_ERROR);
if (!table.same(DatabaseAndTableWithAlias(*table_expression, current_database)))
throw Exception("Inconsistent table names", ErrorCodes::LOGICAL_ERROR);
}
void rewriteCommaToCross()
{
if (join && join->kind == JoinKind::Comma)
join->kind = JoinKind::Cross;
}
JoinKind getOriginalKind() const { return original_kind; }
bool rewriteCrossToInner(ASTPtr on_expression)
{
if (join->kind != JoinKind::Cross)
return false;
join->kind = JoinKind::Inner;
join->strictness = JoinStrictness::All;
join->on_expression = on_expression;
join->children.push_back(join->on_expression);
return true;
}
ASTPtr arrayJoin() const { return element.array_join; }
const ASTTableJoin * tableJoin() const { return join; }
bool canAttachOnExpression() const { return join && !join->on_expression; }
bool hasUsing() const { return join && join->using_expression_list; }
private:
const ASTTablesInSelectQueryElement & element;
ASTTableJoin * join = nullptr;
JoinKind original_kind;
};
bool isAllowedToRewriteCrossJoin(const ASTPtr & node, const Aliases & aliases)
{
if (node->as<ASTFunction>())
{
auto idents = IdentifiersCollector::collect(node);
for (const auto * ident : idents)
{
if (ident->isShort() && aliases.contains(ident->shortName()))
return false;
}
return true;
}
return node->as<ASTIdentifier>() || node->as<ASTLiteral>();
}
/// Return mapping table_no -> expression with expression that can be moved into JOIN ON section
std::map<size_t, std::vector<ASTPtr>> moveExpressionToJoinOn(
const ASTPtr & ast,
const std::vector<JoinedElement> & joined_tables,
const std::vector<TableWithColumnNamesAndTypes> & tables,
const Aliases & aliases)
{
std::map<size_t, std::vector<ASTPtr>> asts_to_join_on;
for (const auto & node : collectConjunctions(ast))
{
if (const auto * func = node->as<ASTFunction>(); func && func->name == NameEquals::name)
{
if (!func->arguments || func->arguments->children.size() != 2)
return {};
/// Check if the identifiers are from different joined tables.
/// If it's a self joint, tables should have aliases.
auto left_table_pos = IdentifierSemantic::getIdentsMembership(func->arguments->children[0], tables, aliases);
auto right_table_pos = IdentifierSemantic::getIdentsMembership(func->arguments->children[1], tables, aliases);
/// Identifiers from different table move to JOIN ON
if (left_table_pos && right_table_pos && *left_table_pos != *right_table_pos)
{
size_t table_pos = std::max(*left_table_pos, *right_table_pos);
if (joined_tables[table_pos].canAttachOnExpression())
asts_to_join_on[table_pos].push_back(node);
else
return {};
}
}
if (!isAllowedToRewriteCrossJoin(node, aliases))
return {};
}
return asts_to_join_on;
}
ASTPtr makeOnExpression(const std::vector<ASTPtr> & expressions)
{
if (expressions.size() == 1)
return expressions[0]->clone();
std::vector<ASTPtr> arguments;
arguments.reserve(expressions.size());
for (const auto & ast : expressions)
arguments.emplace_back(ast->clone());
return makeASTFunction(NameAnd::name, std::move(arguments));
}
std::vector<JoinedElement> getTables(const ASTSelectQuery & select)
{
if (!select.tables())
return {};
const auto * tables = select.tables()->as<ASTTablesInSelectQuery>();
if (!tables)
return {};
size_t num_tables = tables->children.size();
if (num_tables < 2)
return {};
std::vector<JoinedElement> joined_tables;
joined_tables.reserve(num_tables);
bool has_using = false;
for (const auto & child : tables->children)
{
const auto * table_element = child->as<ASTTablesInSelectQueryElement>();
if (!table_element)
throw Exception("Logical error: TablesInSelectQueryElement expected", ErrorCodes::LOGICAL_ERROR);
JoinedElement & t = joined_tables.emplace_back(*table_element);
t.rewriteCommaToCross();
if (t.arrayJoin())
return {};
if (t.hasUsing())
{
if (has_using)
throw Exception(ErrorCodes::NOT_IMPLEMENTED, "Multuple USING statements are not supported");
has_using = true;
}
if (const auto * join = t.tableJoin(); join && isCrossOrComma(join->kind))
{
if (!join->children.empty())
throw Exception(
ErrorCodes::LOGICAL_ERROR, "CROSS JOIN has {} expressions: [{}, ...]",
join->children.size(), queryToString(join->children[0]));
}
}
return joined_tables;
}
}
bool CrossToInnerJoinMatcher::needChildVisit(ASTPtr & node, const ASTPtr &)
{
return !node->as<ASTSubquery>();
}
void CrossToInnerJoinMatcher::visit(ASTPtr & ast, Data & data)
{
if (auto * t = ast->as<ASTSelectQuery>())
visit(*t, ast, data);
}
void CrossToInnerJoinMatcher::visit(ASTSelectQuery & select, ASTPtr &, Data & data)
{
std::vector<JoinedElement> joined_tables = getTables(select);
if (joined_tables.empty())
return;
/// Check if joined_tables are consistent with known tables_with_columns
{
if (joined_tables.size() != data.tables_with_columns.size())
throw Exception(ErrorCodes::LOGICAL_ERROR,
"Logical error: inconsistent number of tables: {} != {}",
joined_tables.size(), data.tables_with_columns.size());
for (size_t i = 0; i < joined_tables.size(); ++i)
joined_tables[i].checkTableName(data.tables_with_columns[i].table, data.current_database);
}
/// CROSS to INNER
if (data.cross_to_inner_join_rewrite && select.where())
{
auto asts_to_join_on = moveExpressionToJoinOn(select.where(), joined_tables, data.tables_with_columns, data.aliases);
for (size_t i = 1; i < joined_tables.size(); ++i)
{
auto & joined = joined_tables[i];
if (joined.tableJoin()->kind != JoinKind::Cross)
continue;
String query_before = queryToString(*joined.tableJoin());
bool rewritten = false;
const auto & expr_it = asts_to_join_on.find(i);
if (expr_it != asts_to_join_on.end())
{
ASTPtr on_expr = makeOnExpression(expr_it->second);
if (rewritten = joined.rewriteCrossToInner(on_expr); rewritten)
{
LOG_DEBUG(&Poco::Logger::get("CrossToInnerJoin"), "Rewritten '{}' to '{}'", query_before, queryToString(*joined.tableJoin()));
}
}
if (joined.getOriginalKind() == JoinKind::Comma &&
data.cross_to_inner_join_rewrite > 1 &&
!rewritten)
{
throw Exception(
ErrorCodes::INCORRECT_QUERY,
"Failed to rewrite comma join to INNER. "
"Please, try to simplify WHERE section "
"or set the setting `cross_to_inner_join_rewrite` to 1 to allow slow CROSS JOIN for this case "
"(cannot rewrite '{} WHERE {}' to INNER JOIN)",
query_before, queryToString(select.where()));
}
}
}
}
}