MDEV-28883 Re-design the upper level of handling UPDATE and DELETE statements

This patch introduces a new way of handling UPDATE and DELETE commands at
the top level after the parsing phase. This new way of processing update
and delete statements can be seen in the implementation of the  prepare()
and execute() methods from the new Sql_cmd_dml class. This class derived
from the Sql_cmd class can be considered as an interface class for processing
such commands as SELECT, INSERT, UPDATE, DELETE and other comands
manipulating data in tables.
With this patch processing of update and delete statements after parsing
proceeds by the following schema:
  - precheck of the access rights is performed for the used tables
  - the used tables are opened
  - context analysis phase is performed for the statement
  - the used tables are locked
  - the statement is optimized and executed
  - clean-up is performed for the statement
The implementation of the method Sql_cmd_dml::execute() adheres this schema.
The virtual functions of the class Sql_cmd_dml used for precheck of the
access rights, context analysis, optimization and execution allow to adjust
this schema for processing data manipulation statements of any types.

This schema of processing data manipulation statements is taken from the
current MySQL code. Moreover the definition the class Sql_cmd_dml introduced
in this patch is almost a full replica of such class in the existing MySQL.
However the implementation of the derived classes for update and delete
statements is quite different. This implementation employs the JOIN class
for all kinds of update and delete statements. It allows to perform main
bulk of context analysis actions by the function JOIN::prepare(). This
guarantees that characteristics and properties of the statement tree
discovered for optimization phase when doing context analysis are the same
for single-table and multi-table updates and deletes.

With this patch the following functions are gone:
  mysql_prepare_update(), mysql_multi_update_prepare(),
  mysql_update(), mysql_multi_update(),
  mysql_prepare_delete(), mysql_multi_delete_prepare(), mysql_delete().
The code within these functions have been used as much as possible though.
The functions mysql_test_update() and mysql_test_delete() are also not
needed anymore. The method Sql_cmd_dml::prepare() serves processing
  - update/delete statement
  - PREPARE stmt FROM "<update/delete statement>"
  - EXECUTE stmt when stmt is prepared from update/delete statement.

Approved by Oleksandr Byelkin <sanja@mariadb.com>

1 files changed, 15 insertions, 0 deletions

diff --git a/sql/sql_base.h b/sql/sql_base.h
index 6e17d8214ad..f4a49d99125 100644
--- a/sql/sql_base.h
+++ b/sql/sql_base.h
@@ -28,6 +28,7 @@ struct Name_resolution_context;
 class Open_table_context;
 class Open_tables_state;
 class Prelocking_strategy;
+class DML_prelocking_strategy;
 struct TABLE_LIST;
 class THD;
 struct handlerton;
@@ -288,6 +289,9 @@ bool open_normal_and_derived_tables(THD *thd, TABLE_LIST *tables, uint flags,
 bool open_tables_only_view_structure(THD *thd, TABLE_LIST *tables,
                                      bool can_deadlock);
 bool open_and_lock_internal_tables(TABLE *table, bool lock);
+bool open_tables_for_query(THD *thd, TABLE_LIST *tables,
+                           uint *table_count, uint flags,
+                           DML_prelocking_strategy *prelocking_strategy);
 bool lock_tables(THD *thd, TABLE_LIST *tables, uint counter, uint flags);
 int decide_logging_format(THD *thd, TABLE_LIST *tables);
 void close_thread_table(THD *thd, TABLE **table_ptr);
@@ -430,6 +434,17 @@ public:
 };
 
 
+
+class Multiupdate_prelocking_strategy : public DML_prelocking_strategy
+{
+  bool done;
+  bool has_prelocking_list;
+public:
+  void reset(THD *thd);
+  bool handle_end(THD *thd);
+};
+
+
 /**
   A strategy for prelocking algorithm to be used for LOCK TABLES
   statement.