ClickHouse/src/Interpreters/InterpreterRenameQuery.h

#pragma once

#include <Interpreters/IInterpreter.h>
#include <Parsers/ASTRenameQuery.h>


namespace DB
{

class Context;
class AccessRightsElements;
class DDLGuard;

/// To avoid deadlocks, we must acquire locks for tables in same order in any different RENAMES.
struct UniqueTableName
{
    String database_name;
    String table_name;

    UniqueTableName(const String & database_name_, const String & table_name_)
            : database_name(database_name_), table_name(table_name_) {}

    bool operator< (const UniqueTableName & rhs) const
    {
        return std::tie(database_name, table_name) < std::tie(rhs.database_name, rhs.table_name);
    }
};

struct RenameDescription
{
    RenameDescription(const ASTRenameQuery::Element & elem, const String & current_database) :
            from_database_name(elem.from.database.empty() ? current_database : elem.from.database),
            from_table_name(elem.from.table),
            to_database_name(elem.to.database.empty() ? current_database : elem.to.database),
            to_table_name(elem.to.table)
    {}

    String from_database_name;
    String from_table_name;

    String to_database_name;
    String to_table_name;
};

using RenameDescriptions = std::vector<RenameDescription>;

using TableGuards = std::map<UniqueTableName, std::unique_ptr<DDLGuard>>;

/** Rename one table
  *  or rename many tables at once.
  */
class InterpreterRenameQuery : public IInterpreter
{
public:
    InterpreterRenameQuery(const ASTPtr & query_ptr_, Context & context_);
    BlockIO execute() override;
    void extendQueryLogElemImpl(QueryLogElement & elem, const ASTPtr & ast, const Context &) const override;

private:
    BlockIO executeToTables(const ASTRenameQuery & rename, const RenameDescriptions & descriptions);
    static BlockIO executeToDatabase(const ASTRenameQuery & rename, const RenameDescriptions & descriptions);

    AccessRightsElements getRequiredAccess() const;

    ASTPtr query_ptr;
    Context & context;

    /// Don't allow to drop tables (that we are renaming); don't allow to create tables in places where tables will be renamed.
    TableGuards table_guards;
};

}