ClickHouse/dbms/src/Storages/StorageView.cpp

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#include <Interpreters/InterpreterSelectQuery.h>
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#include <Interpreters/InterpreterSelectWithUnionQuery.h>
#include <Parsers/ASTCreateQuery.h>
#include <Parsers/ASTSubquery.h>
#include <Storages/StorageView.h>
#include <Storages/StorageFactory.h>
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#include <DataStreams/MaterializingBlockInputStream.h>
#include <Common/typeid_cast.h>
#include <Interpreters/PredicateExpressionsOptimizer.h>
#include <Parsers/ASTAsterisk.h>
#include <iostream>
#include <Parsers/queryToString.h>
namespace DB
{
namespace ErrorCodes
{
extern const int INCORRECT_QUERY;
extern const int LOGICAL_ERROR;
}
StorageView::StorageView(
const String & table_name_,
const ASTCreateQuery & query,
const ColumnsDescription & columns_)
: IStorage{columns_}, table_name(table_name_)
{
if (!query.select)
throw Exception("SELECT query is not specified for " + getName(), ErrorCodes::INCORRECT_QUERY);
inner_query = query.select->ptr();
}
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BlockInputStreams StorageView::read(
const Names & column_names,
const SelectQueryInfo & query_info,
const Context & context,
QueryProcessingStage::Enum /*processed_stage*/,
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const size_t /*max_block_size*/,
const unsigned /*num_streams*/)
{
BlockInputStreams res;
ASTPtr current_inner_query = inner_query;
if (context.getSettings().enable_optimize_predicate_expression)
{
auto new_inner_query = inner_query->clone();
auto new_outer_query = query_info.query->clone();
auto new_outer_select = typeid_cast<ASTSelectQuery *>(new_outer_query.get());
replaceTableNameWithSubquery(new_outer_select, new_inner_query);
if (PredicateExpressionsOptimizer(new_outer_select, context.getSettings(), context).optimize())
current_inner_query = new_inner_query;
}
res = InterpreterSelectWithUnionQuery(current_inner_query, context, column_names).executeWithMultipleStreams();
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/// It's expected that the columns read from storage are not constant.
/// Because method 'getSampleBlockForColumns' is used to obtain a structure of result in InterpreterSelectQuery.
for (auto & stream : res)
stream = std::make_shared<MaterializingBlockInputStream>(stream);
return res;
}
void StorageView::replaceTableNameWithSubquery(ASTSelectQuery * select_query, ASTPtr & subquery)
{
ASTTablesInSelectQueryElement * select_element = static_cast<ASTTablesInSelectQueryElement *>(select_query->tables->children[0].get());
if (!select_element->table_expression)
throw Exception("Logical error: incorrect table expression", ErrorCodes::LOGICAL_ERROR);
ASTTableExpression * table_expression = static_cast<ASTTableExpression *>(select_element->table_expression.get());
if (!table_expression->database_and_table_name)
throw Exception("Logical error: incorrect table expression", ErrorCodes::LOGICAL_ERROR);
const auto alias = table_expression->database_and_table_name->tryGetAlias();
table_expression->database_and_table_name = {};
table_expression->subquery = std::make_shared<ASTSubquery>();
table_expression->subquery->children.push_back(subquery);
if (!alias.empty())
table_expression->subquery->setAlias(alias);
}
void registerStorageView(StorageFactory & factory)
{
factory.registerStorage("View", [](const StorageFactory::Arguments & args)
{
if (args.query.storage)
throw Exception("Specifying ENGINE is not allowed for a View", ErrorCodes::INCORRECT_QUERY);
return StorageView::create(args.table_name, args.query, args.columns);
});
}
}