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Updated QueryAliasVisitor to set prefer_alias_to_column_name for aliases like _subquery

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This commit is contained in:
Maksim Kita 2021-04-20 13:16:29 +03:00
parent 9679bdd86e
commit cbc34afd55
2 changed files with 40 additions and 10 deletions
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2
src/Interpreters/ClusterProxy/SelectStreamFactory.cpp
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@ -160,7 +160,7 @@ void SelectStreamFactory::createForShard(
const auto & settings = context->getSettingsRef();
if ((settings.prefer_localhost_replica && shard_info.isLocal()) || !shard_info.hasRemoteConnections())
if (settings.prefer_localhost_replica && shard_info.isLocal())
{
StoragePtr main_table_storage;

34
src/Interpreters/QueryAliasesVisitor.cpp
View File

@ -15,8 +15,13 @@ namespace ErrorCodes
extern const int MULTIPLE_EXPRESSIONS_FOR_ALIAS;
}
static String wrongAliasMessage(const ASTPtr & ast, const ASTPtr & prev_ast, const String & alias)
namespace
{
constexpr auto dummy_subquery_name_prefix = "_subquery";
String wrongAliasMessage(const ASTPtr & ast, const ASTPtr & prev_ast, const String & alias)
{
WriteBufferFromOwnString message;
message << "Different expressions with the same alias " << backQuoteIfNeed(alias) << ":\n";
formatAST(*ast, message, false, true);
@ -24,6 +29,8 @@ static String wrongAliasMessage(const ASTPtr & ast, const ASTPtr & prev_ast, con
formatAST(*prev_ast, message, false, true);
message << '\n';
return message.str();
}
}
@ -99,7 +106,7 @@ void QueryAliasesMatcher<T>::visit(const ASTSubquery & const_subquery, const AST
String alias;
do
{
alias = "_subquery" + std::to_string(++subquery_index);
alias = dummy_subquery_name_prefix + std::to_string(++subquery_index);
}
while (aliases.count(alias));
@ -124,6 +131,29 @@ void QueryAliasesMatcher<T>::visitOther(const ASTPtr & ast, Data & data)
aliases[alias] = ast;
}
/** QueryAliasesVisitor is executed before ExecuteScalarSubqueriesVisitor.
For example we have subquery in our query (SELECT sum(number) FROM numbers(10)).
After running QueryAliasesVisitor it will be (SELECT sum(number) FROM numbers(10)) as _subquery_1
and prefer_alias_to_column_name for this subquery will be true.
After running ExecuteScalarSubqueriesVisitor it will be converted to (45 as _subquery_1)
and prefer_alias_to_column_name for ast literal will be true.
But if we send such query on remote host with Distributed engine for example we cannot send prefer_alias_to_column_name
information for our ast node with query string. And this alias will be dropped because prefer_alias_to_column_name for ASTWIthAlias
by default is false.
It is imporant that subquery can be converted to literal during ExecuteScalarSubqueriesVisitor.
And code below check if we previously set for subquery alias as _subquery, and if it is true then set prefer_alias_to_column_name = true.
*/
if (auto * ast_with_alias = dynamic_cast<ASTWithAlias *>(ast.get()))
{
if (startsWith(alias, dummy_subquery_name_prefix))
ast_with_alias->prefer_alias_to_column_name = true;
}
}
/// Explicit template instantiations