MDEV-23825 Join select_handler and Pushdown_select + XPand changes

sql/select_handler.cc

@@ -21,10 +21,10 @@
 
 
 /**
-  The methods of the Pushdown_select class.
+  The methods of the select_handler class.
 
   The objects of this class are used for pushdown of the select queries
-  into engines. The main  method of the class is Pushdown_select::execute()
+  into engines. The main  method of the class is select_handler::execute()
   that initiates execution of a select query by a foreign engine, receives the
   rows of the result set, put it in a buffer of a temporary table and send
   them from the buffer directly into output.
@@ -36,51 +36,55 @@
 */
 
 
-Pushdown_select::Pushdown_select(SELECT_LEX *sel, select_handler *h)
-  : select(sel), handler(h)
-{
-  is_analyze= handler->thd->lex->analyze_stmt;
-}
+select_handler::select_handler(THD *thd_arg, handlerton *ht_arg)
+ : thd(thd_arg), ht(ht_arg), table(NULL),
+   is_analyze(thd_arg->lex->analyze_stmt)
+{}
 
 
-Pushdown_select::~Pushdown_select()
+select_handler::~select_handler()
 {
-  if (handler->table)
-    free_tmp_table(handler->thd, handler->table);
-  delete handler;
-  select->select_h= NULL;
+  if (table)
+    free_tmp_table(thd, table);
 }
 
 
-bool Pushdown_select::init()
+TABLE *select_handler::create_tmp_table(THD *thd, SELECT_LEX *select)
 {
+  DBUG_ENTER("select_handler::create_tmp_table");
   List<Item> types;
   TMP_TABLE_PARAM tmp_table_param;
-  THD *thd= handler->thd;
-  DBUG_ENTER("Pushdown_select::init");
   if (select->master_unit()->join_union_item_types(thd, types, 1))
-    DBUG_RETURN(true);
+    DBUG_RETURN(NULL);
   tmp_table_param.init();
   tmp_table_param.field_count= types.elements;
 
-  handler->table= create_tmp_table(thd, &tmp_table_param, types,
+  TABLE *table= ::create_tmp_table(thd, &tmp_table_param, types,
                                    (ORDER *) 0, false, 0,
                                    TMP_TABLE_ALL_COLUMNS, 1,
                                    &empty_clex_str, true, false);
-  if (!handler->table)
-    DBUG_RETURN(true);
-  if (handler->table->fill_item_list(&result_columns))
+  DBUG_RETURN(table);
+}
+
+
+bool select_handler::prepare()
+{
+  DBUG_ENTER("select_handler::prepare");
+  /*
+    Some engines (e.g. XPand) initialize "table" on their own.
+    So we need to create a temporary table only if "table" is NULL.
+  */
+  if (!table && !(table= create_tmp_table(thd, select)))
     DBUG_RETURN(true);
-  DBUG_RETURN(false);
+  DBUG_RETURN(table->fill_item_list(&result_columns));
 }
 
 
-bool Pushdown_select::send_result_set_metadata()
+bool select_handler::send_result_set_metadata()
 {
-  DBUG_ENTER("Pushdown_select::send_result_set_metadata");
+  DBUG_ENTER("select_handler::send_result_set_metadata");
 
 #ifdef WITH_WSREP
-  THD *thd= handler->thd;
   if (WSREP(thd) && thd->wsrep_retry_query)
   {
     WSREP_DEBUG("skipping select metadata");
@@ -96,7 +100,7 @@ bool Pushdown_select::send_result_set_metadata()
 }
 
 
-bool Pushdown_select::send_data()
+bool select_handler::send_data()
 {
   DBUG_ENTER("Pushdown_select::send_data");
 
@@ -107,48 +111,47 @@ bool Pushdown_select::send_data()
 }
 
 
-bool Pushdown_select::send_eof()
+bool select_handler::send_eof()
 {
-  DBUG_ENTER("Pushdown_select::send_eof");
+  DBUG_ENTER("select_handler::send_eof");
 
   if (select->join->result->send_eof())
     DBUG_RETURN(true);
   DBUG_RETURN(false);
 }
 
 
-int Pushdown_select::execute()
+int select_handler::execute()
 {
   int err;
-  THD *thd= handler->thd;
 
-  DBUG_ENTER("Pushdown_select::execute");
+  DBUG_ENTER("select_handler::execute");
 
-  if ((err= handler->init_scan()))
+  if ((err= init_scan()))
     goto error;
 
   if (is_analyze)
   {
-    handler->end_scan();
+    end_scan();
     DBUG_RETURN(0);
   }
 
   if (send_result_set_metadata())
     DBUG_RETURN(-1);
 
-  while (!(err= handler->next_row()))
+  while (!(err= next_row()))
   {
     if (thd->check_killed() || send_data())
     {
-      handler->end_scan();
+      end_scan();
       DBUG_RETURN(-1);
     }
   }
 
   if (err != 0 && err != HA_ERR_END_OF_FILE)
     goto error;
 
-  if ((err= handler->end_scan()))
+  if ((err= end_scan()))
    goto error_2;
 
   if (send_eof())
@@ -157,9 +160,9 @@ int Pushdown_select::execute()
   DBUG_RETURN(0);
 
 error:
-  handler->end_scan();
+  end_scan();
 error_2:
-  handler->print_error(err, MYF(0));
+  print_error(err, MYF(0));
   DBUG_RETURN(-1);                              // Error not sent to client
 }
 

sql/select_handler.h

@@ -41,12 +41,24 @@ class select_handler
     The table is actually never filled. Only its record buffer is used.
   */
   TABLE *table;
+  List<Item> result_columns;
 
-  select_handler(THD *thd_arg, handlerton *ht_arg)
-    : thd(thd_arg), ht(ht_arg), table(0) {}
+  bool is_analyze;
 
-  virtual ~select_handler() {}
+  bool send_result_set_metadata();
+  bool send_data();
 
+  select_handler(THD *thd_arg, handlerton *ht_arg);
+
+  virtual ~select_handler();
+
+  int execute();
+
+  virtual bool prepare();
+
+  static TABLE *create_tmp_table(THD *thd, SELECT_LEX *sel);
+
+protected:
   /*
     Functions to scan the select result set.
     All these returns 0 if ok, error code in case of error.
@@ -67,6 +79,8 @@ class select_handler
 
   /* Report errors */
   virtual void print_error(int error, myf errflag);
+
+  bool send_eof();
 };
 
 #endif /* SELECT_HANDLER_INCLUDED */

sql/sql_lex.h

@@ -1334,10 +1334,8 @@ class st_select_lex: public st_select_lex_node
   table_value_constr *tvc;
   bool in_tvc;
 
-  /* The interface employed to execute the select query by a foreign engine */
-  select_handler *select_h;
   /* The object used to organize execution of the query by a foreign engine */
-  Pushdown_select *pushdown_select;
+  select_handler *pushdown_select;
 
   /** System Versioning */
 public:

sql/sql_select.cc

@@ -1608,7 +1608,7 @@ int JOIN::optimize()
     if (!(select_options & SELECT_DESCRIBE))
     {
       /* Prepare to execute the query pushed into a foreign engine */
-      res= select_lex->pushdown_select->init();
+      res= select_lex->pushdown_select->prepare();
     }
     with_two_phase_optimization= false;
   }
@@ -4632,19 +4632,7 @@ mysql_select(THD *thd, TABLE_LIST *tables, List<Item> &fields, COND *conds,
   }
 
   /* Look for a table owned by an engine with the select_handler interface */
-  select_lex->select_h= select_lex->find_select_handler(thd);
-  if (select_lex->select_h)
-  {
-    /* Create a Pushdown_select object for later execution of the query */
-    if (!(select_lex->pushdown_select=
-      new (thd->mem_root) Pushdown_select(select_lex,
-                                          select_lex->select_h)))
-    {
-      delete select_lex->select_h;
-      select_lex->select_h= NULL;
-      DBUG_RETURN(TRUE);
-    }
-  }
+  select_lex->pushdown_select= select_lex->find_select_handler(thd);
 
   if ((err= join->optimize()))
   {

sql/sql_select.h

@@ -2517,29 +2517,6 @@ class Pushdown_derived: public Sql_alloc
 class select_handler;
 
 
-class Pushdown_select: public Sql_alloc
-{
-private:
-  bool is_analyze;
-  List<Item> result_columns;
-  bool send_result_set_metadata();
-  bool send_data();
-  bool send_eof();
-
-public:
-  SELECT_LEX *select;
-  select_handler *handler;
-
-  Pushdown_select(SELECT_LEX *sel, select_handler *h);
-
-  ~Pushdown_select();
-
-  bool init();
-
-  int execute(); 
-};
-
-
 bool test_if_order_compatible(SQL_I_List<ORDER> &a, SQL_I_List<ORDER> &b);
 int test_if_group_changed(List<Cached_item> &list);
 int create_sort_index(THD *thd, JOIN *join, JOIN_TAB *tab, Filesort *fsort);