Simplify NEXTVAL(sequence) when used with DEFAULT

Instead of adding another TABLE_LIST to
Item_func_nextval->table_list->next_local, update instead
Item_func_nextval->table_list->table with the correct table.

This removes all checking of table_list->table and table_list->next_local
when using sequences.

Author: montywi

sql/item_func.h

@@ -4448,7 +4448,7 @@ class Item_func_nextval :public Item_longlong_func
   bool check_access(THD *, privilege_t);
 public:
   Item_func_nextval(THD *thd, TABLE_LIST *table_list_arg):
-  Item_longlong_func(thd), table_list(table_list_arg) {}
+  Item_longlong_func(thd), table_list(table_list_arg), table(0) {}
   longlong val_int() override;
   LEX_CSTRING func_name_cstring() const override
   {
@@ -4478,14 +4478,8 @@ class Item_func_nextval :public Item_longlong_func
   */
   void update_table()
   {
-    if (!(table= table_list->table))
-    {
-      /*
-        If nextval was used in DEFAULT then next_local points to
-        the table_list used by to open the sequence table
-      */
-      table= table_list->next_local->table;
-    }
+    table= table_list->table;
+    DBUG_ASSERT(table);
   }
   bool const_item() const override { return 0; }
   Item *do_get_copy(THD *thd) const override

sql/sql_base.cc

@@ -2446,6 +2446,11 @@ bool open_table(THD *thd, TABLE_LIST *table_list, Open_table_context *ot_ctx)
   DBUG_ASSERT(table->file->pushed_cond == NULL);
   table_list->updatable= 1; // It is not derived table nor non-updatable VIEW
   table_list->table= table;
+  if (table_list->linked_table)
+  {
+    /* Update link for sequence tables in default */
+    table_list->linked_table->table= table;
+  }
 
   if (!from_share && table->vcol_fix_expr(thd))
     DBUG_RETURN(true);
@@ -5068,7 +5073,7 @@ add_internal_tables(THD *thd, Query_tables_list *prelocking_ctx,
         next_local value as it may have been changed by a previous
         statement using the same table.
       */
-      tables->next_local= tmp;
+      tmp->linked_table= tables;
       continue;
     }
 
@@ -5083,10 +5088,10 @@ add_internal_tables(THD *thd, Query_tables_list *prelocking_ctx,
                                       &prelocking_ctx->query_tables_last,
                                       tables->for_insert_data);
     /*
-      Store link to the new table_list that will be used by open so that
-      Item_func_nextval() can find it
+      Store link to the sequences table so that we can in open_table() update
+      it to point to the opened table.
     */
-    tables->next_local= tl;
+    tl->linked_table= tables;
     DBUG_PRINT("info", ("table name: %s added", tables->table_name.str));
   } while ((tables= tables->next_global));
   DBUG_RETURN(FALSE);

sql/table.h

@@ -2581,6 +2581,7 @@ struct TABLE_LIST
   TABLE_LIST *next_local;
   /* link in a global list of all queries tables */
   TABLE_LIST *next_global, **prev_global;
+  TABLE_LIST *linked_table;             // For sequence tables used in default
   Lex_ident_db db;
   Lex_ident_table table_name;
   Lex_ident_i_s_table schema_table_name;