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2d595319bf
The function was originally introduced by eb0804ef5e
MDEV-18553: MDEV-16327 pre-requisits part 1: isolation of LIMIT/OFFSET handling
set_unlimited had an overloaded notion of both clearing the offset value
and the limit value. The code is used for SQL_CALC_ROWS option to
disable the limit clause after the limit is reached, while at the same
time the calling code suppreses sending of rows.
Proposed solution:
Dedicated clear method for query initialization (to ensure no garbage
remains between executions).
Dedicated set_unlimited that only alters the limit value.
84 lines
2.6 KiB
C++
84 lines
2.6 KiB
C++
/* Copyright (c) 2019, MariaDB Corporation.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; version 2 of the License.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1335 USA */
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#ifndef INCLUDES_MARIADB_SQL_LIMIT_H
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#define INCLUDES_MARIADB_SQL_LIMIT_H
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/**
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LIMIT/OFFSET parameters for execution.
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*/
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class Select_limit_counters
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{
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ha_rows select_limit_cnt, offset_limit_cnt;
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public:
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Select_limit_counters():
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select_limit_cnt(0), offset_limit_cnt(0)
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{};
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Select_limit_counters(Select_limit_counters &orig):
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select_limit_cnt(orig.select_limit_cnt),
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offset_limit_cnt(orig.offset_limit_cnt)
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{};
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void set_limit(ha_rows limit, ha_rows offset)
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{
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offset_limit_cnt= offset;
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select_limit_cnt= limit;
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/*
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Guard against an overflow condition, where limit + offset exceede
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ha_rows value range. This case covers unreasonably large parameter
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values that do not have any practical use so assuming in this case
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that the query does not have a limit is fine.
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*/
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if (select_limit_cnt + offset_limit_cnt >= select_limit_cnt)
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select_limit_cnt+= offset_limit_cnt;
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else
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select_limit_cnt= HA_POS_ERROR;
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}
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void set_single_row()
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{
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offset_limit_cnt= 0;
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select_limit_cnt= 1;
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}
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bool is_unlimited() const
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{ return select_limit_cnt == HA_POS_ERROR; }
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/*
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Set the limit to allow returning an unlimited number of rows. Useful
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for cases when we want to continue execution indefinitely after the limit
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is reached (for example for SQL_CALC_ROWS extension).
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*/
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void set_unlimited()
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{ select_limit_cnt= HA_POS_ERROR; }
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/* Reset the limit entirely. */
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void clear()
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{ select_limit_cnt= HA_POS_ERROR; offset_limit_cnt= 0; }
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bool check_offset(ha_rows sent) const
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{
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return sent < offset_limit_cnt;
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}
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void remove_offset() { offset_limit_cnt= 0; }
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ha_rows get_select_limit() const
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{ return select_limit_cnt; }
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ha_rows get_offset_limit() const
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{ return offset_limit_cnt; }
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};
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#endif // INCLUDES_MARIADB_SQL_LIMIT_H
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