1#@!#!123s

: / usr / include / mysql / server / private /
Filename : sql_limit.h
back
/*  Copyright (c) 2019, MariaDB Corporation.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; version 2 of the License.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1335  USA */


#ifndef INCLUDES_MARIADB_SQL_LIMIT_H
#define INCLUDES_MARIADB_SQL_LIMIT_H
/**
  LIMIT/OFFSET parameters for execution.
*/

class Select_limit_counters
{
  ha_rows select_limit_cnt, offset_limit_cnt;
  bool with_ties;

  public:
    Select_limit_counters():
       select_limit_cnt(0), offset_limit_cnt(0), with_ties(false)
       {};
    Select_limit_counters(const Select_limit_counters &orig):
       select_limit_cnt(orig.select_limit_cnt),
       offset_limit_cnt(orig.offset_limit_cnt),
       with_ties(orig.with_ties)
       {};

   void set_limit(ha_rows limit, ha_rows offset, bool with_ties_arg)
   {
      if (limit == 0)
        offset= 0;
      offset_limit_cnt= offset;
      select_limit_cnt= limit;
      with_ties= with_ties_arg;
      /*
        Guard against an overflow condition, where limit + offset exceede
        ha_rows value range. This case covers unreasonably large parameter
        values that do not have any practical use so assuming in this case
        that the query does not have a limit is fine.
      */
      if (select_limit_cnt + offset_limit_cnt >= select_limit_cnt)
        select_limit_cnt+= offset_limit_cnt;
      else
        select_limit_cnt= HA_POS_ERROR;
   }

   void set_single_row()
   {
     offset_limit_cnt= 0;
     select_limit_cnt= 1;
     with_ties= false;
   }

   /* Send the first row, still honoring offset_limit_cnt */
   void send_first_row()
   {
     /* Guard against overflow */
     if ((select_limit_cnt= offset_limit_cnt +1 ) == 0)
       select_limit_cnt= offset_limit_cnt;
     // with_ties= false;   Remove // on merge to 10.6
   }

   bool is_unlimited() const
   { return select_limit_cnt == HA_POS_ERROR; }
   /*
      Set the limit to allow returning an unlimited number of rows. Useful
      for cases when we want to continue execution indefinitely after the limit
      is reached (for example for SQL_CALC_ROWS extension).
   */
   void set_unlimited()
   { select_limit_cnt= HA_POS_ERROR; }

   /* Reset the limit entirely. */
   void clear()
   { select_limit_cnt= HA_POS_ERROR; offset_limit_cnt= 0; with_ties= false;}

   bool check_offset(ha_rows sent) const
   {
     return sent < offset_limit_cnt;
   }
   void remove_offset() { offset_limit_cnt= 0; }

   ha_rows get_select_limit() const
   { return select_limit_cnt; }
   ha_rows get_offset_limit() const
   { return offset_limit_cnt; }
   bool is_with_ties() const
   { return with_ties; }
};

#endif // INCLUDES_MARIADB_SQL_LIMIT_H