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248 lines
8.0 KiB
248 lines
8.0 KiB
5 months ago
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/* Copyright (c) 2009, 2019, Oracle and/or its affiliates. All rights reserved.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License, version 2.0,
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as published by the Free Software Foundation.
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This program is also distributed with certain software (including
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but not limited to OpenSSL) that is licensed under separate terms,
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as designated in a particular file or component or in included license
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documentation. The authors of MySQL hereby grant you an additional
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permission to link the program and your derivative works with the
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separately licensed software that they have included with MySQL.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License, version 2.0, for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA */
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/**
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@file sql/sql_cmd.h
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Representation of an SQL command.
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*/
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#ifndef SQL_CMD_INCLUDED
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#define SQL_CMD_INCLUDED
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#include "my_dbug.h"
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#include "my_sqlcommand.h"
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#include "sql/select_lex_visitor.h"
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class THD;
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class Prepared_statement;
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struct handlerton;
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struct MYSQL_LEX_STRING;
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struct MYSQL_LEX_CSTRING;
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/**
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Representation of an SQL command.
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This class is an interface between the parser and the runtime.
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The parser builds the appropriate derived classes of Sql_cmd
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to represent a SQL statement in the parsed tree.
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The execute() method in the derived classes of Sql_cmd contain the runtime
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implementation.
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Note that this interface is used for SQL statements recently implemented,
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the code for older statements tend to load the LEX structure with more
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attributes instead.
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Implement new statements by sub-classing Sql_cmd, as this improves
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code modularity (see the 'big switch' in dispatch_command()), and decreases
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the total size of the LEX structure (therefore saving memory in stored
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programs).
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The recommended name of a derived class of Sql_cmd is Sql_cmd_<derived>.
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Notice that the Sql_cmd class should not be confused with the Statement class.
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Statement is a class that is used to manage an SQL command or a set
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of SQL commands. When the SQL statement text is analyzed, the parser will
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create one or more Sql_cmd objects to represent the actual SQL commands.
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*/
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class Sql_cmd {
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private:
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Sql_cmd(const Sql_cmd &); // No copy constructor wanted
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void operator=(Sql_cmd &); // No assignment operator wanted
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public:
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/**
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@brief Return the command code for this statement
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*/
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virtual enum_sql_command sql_command_code() const = 0;
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/// @return true if this statement is prepared
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bool is_prepared() const { return m_prepared; }
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/**
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Prepare this SQL statement.
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@param thd the current thread
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@returns false if success, true if error
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*/
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virtual bool prepare(THD *thd MY_ATTRIBUTE((unused))) {
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// Default behavior for a statement is to have no preparation code.
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/* purecov: begin inspected */
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DBUG_ASSERT(!is_prepared());
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set_prepared();
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return false;
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/* purecov: end */
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}
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/**
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Execute this SQL statement.
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@param thd the current thread.
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@returns false if success, true if error
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*/
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virtual bool execute(THD *thd) = 0;
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/**
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Command-specific reinitialization before execution of prepared statement
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@see reinit_stmt_before_use()
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@note Currently this function is overloaded for INSERT/REPLACE stmts only.
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@param thd Current THD.
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*/
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virtual void cleanup(THD *thd MY_ATTRIBUTE((unused))) {
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m_secondary_engine = nullptr;
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}
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/// Set the owning prepared statement
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void set_owner(Prepared_statement *stmt) { m_owner = stmt; }
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/// Get the owning prepared statement
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Prepared_statement *get_owner() { return m_owner; }
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/// @return true if SQL command is a DML statement
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virtual bool is_dml() const { return false; }
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/// @return true if implemented as single table plan, DML statement only
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virtual bool is_single_table_plan() const {
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/* purecov: begin inspected */
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DBUG_ASSERT(is_dml());
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return false;
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/* purecov: end */
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}
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/**
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Temporary function used to "unprepare" a prepared statement after
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preparation, so that a subsequent execute statement will reprepare it.
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This is done because UNIT::cleanup() will un-resolve all resolved QBs.
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*/
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virtual void unprepare(THD *thd MY_ATTRIBUTE((unused))) {
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DBUG_ASSERT(is_prepared());
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m_prepared = false;
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}
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virtual bool accept(THD *thd MY_ATTRIBUTE((unused)),
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Select_lex_visitor *visitor MY_ATTRIBUTE((unused))) {
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return false;
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}
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/**
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Is this statement of a type and on a form that makes it eligible
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for execution in a secondary storage engine?
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@return the name of the secondary storage engine, or nullptr if
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the statement is not eligible for execution in a secondary storage
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engine
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*/
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virtual const MYSQL_LEX_CSTRING *eligible_secondary_storage_engine() const {
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return nullptr;
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}
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/**
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Disable use of secondary storage engines in this statement. After
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a call to this function, the statement will not try to use a
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secondary storage engine until it is reprepared.
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*/
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void disable_secondary_storage_engine() {
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DBUG_ASSERT(m_secondary_engine == nullptr);
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m_secondary_engine_enabled = false;
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}
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/**
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Has use of secondary storage engines been disabled for this statement?
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*/
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bool secondary_storage_engine_disabled() const {
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return !m_secondary_engine_enabled;
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}
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/**
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Mark the current statement as using a secondary storage engine.
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This function must be called before the statement starts opening
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tables in a secondary engine.
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*/
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void use_secondary_storage_engine(const handlerton *hton) {
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DBUG_ASSERT(m_secondary_engine_enabled);
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m_secondary_engine = hton;
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}
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/**
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Is this statement using a secondary storage engine?
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*/
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bool using_secondary_storage_engine() const {
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return m_secondary_engine != nullptr;
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}
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/**
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Get the handlerton of the secondary engine that is used for
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executing this statement, or nullptr if a secondary engine is not
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used.
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*/
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const handlerton *secondary_engine() const { return m_secondary_engine; }
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protected:
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Sql_cmd() : m_owner(nullptr), m_prepared(false), prepare_only(true) {}
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virtual ~Sql_cmd() {
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/*
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Sql_cmd objects are allocated in thd->mem_root.
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In MySQL, the C++ destructor is never called, the underlying MEM_ROOT is
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simply destroyed instead.
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Do not rely on the destructor for any cleanup.
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*/
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DBUG_ASSERT(false);
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}
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/**
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@return true if object represents a preparable statement, ie. a query
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that is prepared with a PREPARE statement and executed with an EXECUTE
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statement. False is returned for regular statements (non-preparable
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statements) that are executed directly.
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@todo replace with "m_owner != nullptr" when prepare-once is implemented
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*/
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bool needs_explicit_preparation() const { return prepare_only; }
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/// Set this statement as prepared
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void set_prepared() { m_prepared = true; }
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private:
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Prepared_statement
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*m_owner; /// Owning prepared statement, nullptr if non-prep.
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bool m_prepared; /// True when statement has been prepared
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/**
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Tells if a secondary storage engine can be used for this
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statement. If it is false, use of a secondary storage engine will
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not be considered for executing this statement.
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*/
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bool m_secondary_engine_enabled{true};
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/**
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The secondary storage engine to use for execution of this
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statement, if any, or nullptr if the primary engine is used.
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This property is reset at the start of each execution.
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*/
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const handlerton *m_secondary_engine{nullptr};
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protected:
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bool prepare_only; /// @see needs_explicit_preparation
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/// @todo remove when prepare-once is implemented
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};
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#endif // SQL_CMD_INCLUDED
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