test-example-projects/c++_projects/280w-mysql-8.0.18/sql/opt_explain.h

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#ifndef OPT_EXPLAIN_INCLUDED
#define OPT_EXPLAIN_INCLUDED

/**
  @file sql/opt_explain.h
  EXPLAIN @<command@>.

Single table UPDATE/DELETE commands are explained by the
explain_single_table_modification() function.

A query expression (complete SELECT query possibly including
subqueries and unions), INSERT...SELECT and multitable UPDATE/DELETE
commands are explained like this:

(1) explain_query_expression()

Is the entry point. Forwards the job to explain_unit().

(2) explain_unit()

Is for a SELECT_LEX_UNIT, prepares, optimizes, explains one JOIN for
each "top-level" SELECT_LEXs of the unit (like: all SELECTs of a
UNION; but not subqueries), and one JOIN for the fake SELECT_LEX of
UNION); each JOIN explain (JOIN::exec()) calls explain_query_specification()

(3) explain_query_specification()

Is for a single SELECT_LEX (fake or not). It needs a prepared and
optimized JOIN, for which it builds the EXPLAIN rows. But it also
launches the EXPLAIN process for "inner units" (==subqueries of this
SELECT_LEX), by calling explain_unit() for each of them.
*/

#include <string>
#include <vector>

#include "my_base.h"
#include "my_sqlcommand.h"
#include "my_thread_local.h"
#include "sql/opt_explain_format.h"
#include "sql/parse_tree_node_base.h"
#include "sql/query_result.h"  // Query_result_send
#include "sql/row_iterator.h"
#include "sql/sql_cmd.h"  // Sql_cmd
#include "sql/sql_lex.h"
#include "sys/types.h"

#include <functional>
#include <string>

class Item;
class JOIN;
class QEP_TAB;
class SELECT_LEX;
class SELECT_LEX_UNIT;
class THD;
struct TABLE;
template <class T>
class List;

extern const char *join_type_str[];

/** Table modification plan for JOIN-less statements (update/delete) */
class Modification_plan {
 public:
  THD *const thd;  ///< Owning thread
  const enum_mod_type
      mod_type;  ///< Modification type - MT_INSERT/MT_UPDATE/etc
  TABLE *table;  ///< Table to modify

  QEP_TAB *tab;               ///< QUICK access method + WHERE clause
  uint key;                   ///< Key to use
  ha_rows limit;              ///< Limit
  bool need_tmp_table;        ///< Whether tmp table needs to be used
  bool need_sort;             ///< Whether to use filesort
  bool used_key_is_modified;  ///< Whether the key used to scan is modified
  const char *message;        ///< Arbitrary message
  bool zero_result;           ///< true <=> plan will not be executed
  ha_rows examined_rows;  ///< # of rows expected to be examined in the table

  Modification_plan(THD *thd_arg, enum_mod_type mt, QEP_TAB *qep_tab,
                    uint key_arg, ha_rows limit_arg, bool need_tmp_table_arg,
                    bool need_sort_arg, bool used_key_is_modified_arg,
                    ha_rows rows);

  Modification_plan(THD *thd_arg, enum_mod_type mt, TABLE *table_arg,
                    const char *message_arg, bool zero_result_arg,
                    ha_rows rows);

  ~Modification_plan();

 private:
  void register_in_thd();
};

/**
  EXPLAIN functionality for Query_result_insert, Query_result_update and
  Query_result_delete.

  This class objects substitute Query_result_insert, Query_result_update and
  Query_result_delete data interceptor objects to implement EXPLAIN for INSERT,
  REPLACE and multi-table UPDATE and DELETE queries.
  Query_result_explain class object initializes tables like Query_result_insert,
  Query_result_update or Query_result_delete data interceptor do, but it
  suppresses table data modification by the underlying interceptor object.
  Thus, we can use Query_result_explain object in the context of EXPLAIN INSERT/
  REPLACE/UPDATE/DELETE query like we use Query_result_send in the context of
  EXPLAIN SELECT command:
  1) in presence of lex->describe flag, pass Query_result_explain object to
     execution function,
  2) it calls prepare(), optimize() and start_execution() functions
     to mark modified tables etc.
*/

class Query_result_explain final : public Query_result_send {
 protected:
  /**
    Pointer to underlying Query_result_insert, Query_result_update or
    Query_result_delete object.
  */
  Query_result *interceptor;

 public:
  Query_result_explain(SELECT_LEX_UNIT *unit_arg, Query_result *interceptor_arg)
      : Query_result_send(), interceptor(interceptor_arg) {
    unit = unit_arg;
  }

 protected:
  bool prepare(THD *thd, List<Item> &list, SELECT_LEX_UNIT *u) override {
    return Query_result_send::prepare(thd, list, u) ||
           interceptor->prepare(thd, list, u);
  }

  bool start_execution(THD *thd) override {
    return Query_result_send::start_execution(thd) ||
           interceptor->start_execution(thd);
  }

  bool optimize() override {
    return Query_result_send::optimize() || interceptor->optimize();
  }

  void cleanup(THD *thd) override {
    Query_result_send::cleanup(thd);
    interceptor->cleanup(thd);
  }
};

bool explain_no_table(THD *explain_thd, const THD *query_thd,
                      SELECT_LEX *select_lex, const char *message,
                      enum_parsing_context ctx);
bool explain_single_table_modification(THD *explain_thd, const THD *query_thd,
                                       const Modification_plan *plan,
                                       SELECT_LEX *select);
bool explain_query(THD *explain_thd, const THD *query_thd,
                   SELECT_LEX_UNIT *unit);
bool explain_query_specification(THD *explain_thd, const THD *query_thd,
                                 SELECT_LEX *select_lex,
                                 enum_parsing_context ctx);

class Sql_cmd_explain_other_thread final : public Sql_cmd {
 public:
  explicit Sql_cmd_explain_other_thread(my_thread_id thread_id)
      : m_thread_id(thread_id) {}

  enum_sql_command sql_command_code() const override {
    return SQLCOM_EXPLAIN_OTHER;
  }

  bool execute(THD *thd) override;

 private:
  /// connection_id in EXPLAIN FOR CONNECTION \<connection_id\>
  my_thread_id m_thread_id;
};

// Print out an iterator and all of its children (if any) in a tree.
// "level" is the current indenting level, as this is called recursively.
std::string PrintQueryPlan(int level, RowIterator *iterator);

// For each subselect within the given item, call the given functor
// with its SELECT number, dependent/cacheable status and an iterator
// (or nullptr if none; this may happen if the query is not executable
// by the iterator executor).
void ForEachSubselect(
    Item *parent_item,
    const std::function<void(int select_number, bool is_dependent,
                             bool is_cacheable, RowIterator *iterator)>
        &callback);

// For the given join, return a list of pseudo-children corresponding to
// subselects in the SELECT list (if any).
std::vector<RowIterator::Child> GetIteratorsFromSelectList(JOIN *join);

#endif /* OPT_EXPLAIN_INCLUDED */