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https://github.com/MariaDB/server.git
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1033 lines
34 KiB
C++
1033 lines
34 KiB
C++
/* Copyright (c) 2000, 2011, Oracle and/or its affiliates.
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Copyright (c) 2008-2011 Monty Program Ab
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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 02110-1301 USA
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*/
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/**
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@file
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Optimising of MIN(), MAX() and COUNT(*) queries without 'group by' clause
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by replacing the aggregate expression with a constant.
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Given a table with a compound key on columns (a,b,c), the following
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types of queries are optimised (assuming the table handler supports
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the required methods)
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@verbatim
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SELECT COUNT(*) FROM t1[,t2,t3,...]
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SELECT MIN(b) FROM t1 WHERE a=const
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SELECT MAX(c) FROM t1 WHERE a=const AND b=const
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SELECT MAX(b) FROM t1 WHERE a=const AND b<const
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SELECT MIN(b) FROM t1 WHERE a=const AND b>const
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SELECT MIN(b) FROM t1 WHERE a=const AND b BETWEEN const AND const
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SELECT MAX(b) FROM t1 WHERE a=const AND b BETWEEN const AND const
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@endverbatim
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Instead of '<' one can use '<=', '>', '>=' and '=' as well.
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Instead of 'a=const' the condition 'a IS NULL' can be used.
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If all selected fields are replaced then we will also remove all
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involved tables and return the answer without any join. Thus, the
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following query will be replaced with a row of two constants:
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@verbatim
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SELECT MAX(b), MIN(d) FROM t1,t2
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WHERE a=const AND b<const AND d>const
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@endverbatim
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(assuming a index for column d of table t2 is defined)
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*/
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#include "mysql_priv.h"
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#include "sql_select.h"
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static bool find_key_for_maxmin(bool max_fl, TABLE_REF *ref, Field* field,
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COND *cond, uint *range_fl,
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uint *key_prefix_length);
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static int reckey_in_range(bool max_fl, TABLE_REF *ref, Field* field,
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COND *cond, uint range_fl, uint prefix_len);
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static int maxmin_in_range(bool max_fl, Field* field, COND *cond);
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/*
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Get exact count of rows in all tables
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SYNOPSIS
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get_exact_records()
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tables List of tables
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NOTES
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When this is called, we know all table handlers supports HA_HAS_RECORDS
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or HA_STATS_RECORDS_IS_EXACT
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RETURN
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ULONGLONG_MAX Error: Could not calculate number of rows
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# Multiplication of number of rows in all tables
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*/
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static ulonglong get_exact_record_count(List<TABLE_LIST> &tables)
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{
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ulonglong count= 1;
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TABLE_LIST *tl;
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List_iterator<TABLE_LIST> ti(tables);
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while ((tl= ti++))
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{
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ha_rows tmp= tl->table->file->records();
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if ((tmp == HA_POS_ERROR))
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return ULONGLONG_MAX;
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count*= tmp;
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}
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return count;
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}
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/**
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Use index to read MIN(field) value.
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@param table Table object
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@param ref Reference to the structure where we store the key value
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@item_field Field used in MIN()
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@range_fl Whether range endpoint is strict less than
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@prefix_len Length of common key part for the range
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@retval
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0 No errors
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HA_ERR_... Otherwise
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*/
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static int get_index_min_value(TABLE *table, TABLE_REF *ref,
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Item_field *item_field, uint range_fl,
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uint prefix_len)
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{
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int error;
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if (!ref->key_length)
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error= table->file->ha_index_first(table->record[0]);
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else
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{
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/*
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Use index to replace MIN/MAX functions with their values
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according to the following rules:
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1) Insert the minimum non-null values where the WHERE clause still
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matches, or
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2) a NULL value if there are only NULL values for key_part_k.
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3) Fail, producing a row of nulls
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Implementation: Read the smallest value using the search key. If
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the interval is open, read the next value after the search
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key. If read fails, and we're looking for a MIN() value for a
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nullable column, test if there is an exact match for the key.
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*/
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if (!(range_fl & NEAR_MIN))
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/*
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Closed interval: Either The MIN argument is non-nullable, or
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we have a >= predicate for the MIN argument.
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*/
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error= table->file->ha_index_read_map(table->record[0],
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ref->key_buff,
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make_prev_keypart_map(ref->key_parts),
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HA_READ_KEY_OR_NEXT);
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else
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{
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/*
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Open interval: There are two cases:
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1) We have only MIN() and the argument column is nullable, or
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2) there is a > predicate on it, nullability is irrelevant.
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We need to scan the next bigger record first.
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Open interval is not used if the search key involves the last keypart,
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and it would not work.
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*/
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DBUG_ASSERT(prefix_len < ref->key_length);
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error= table->file->ha_index_read_map(table->record[0],
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ref->key_buff,
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make_prev_keypart_map(ref->key_parts),
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HA_READ_AFTER_KEY);
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/*
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If the found record is outside the group formed by the search
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prefix, or there is no such record at all, check if all
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records in that group have NULL in the MIN argument
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column. If that is the case return that NULL.
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Check if case 1 from above holds. If it does, we should read
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the skipped tuple.
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*/
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if (item_field->field->real_maybe_null() &&
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ref->key_buff[prefix_len] == 1 &&
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/*
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Last keypart (i.e. the argument to MIN) is set to NULL by
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find_key_for_maxmin only if all other keyparts are bound
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to constants in a conjunction of equalities. Hence, we
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can detect this by checking only if the last keypart is
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NULL.
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*/
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(error == HA_ERR_KEY_NOT_FOUND ||
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key_cmp_if_same(table, ref->key_buff, ref->key, prefix_len)))
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{
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DBUG_ASSERT(item_field->field->real_maybe_null());
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error= table->file->ha_index_read_map(table->record[0],
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ref->key_buff,
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make_prev_keypart_map(ref->key_parts),
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HA_READ_KEY_EXACT);
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}
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}
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}
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return error;
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}
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/**
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Use index to read MAX(field) value.
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@param table Table object
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@param ref Reference to the structure where we store the key value
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@range_fl Whether range endpoint is strict greater than
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@retval
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0 No errors
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HA_ERR_... Otherwise
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*/
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static int get_index_max_value(TABLE *table, TABLE_REF *ref, uint range_fl)
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{
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return (ref->key_length ?
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table->file->ha_index_read_map(table->record[0], ref->key_buff,
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make_prev_keypart_map(ref->key_parts),
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range_fl & NEAR_MAX ?
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HA_READ_BEFORE_KEY :
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HA_READ_PREFIX_LAST_OR_PREV) :
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table->file->ha_index_last(table->record[0]));
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}
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/**
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Substitutes constants for some COUNT(), MIN() and MAX() functions.
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@param thd thread handler
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@param tables list of leaves of join table tree
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@param all_fields All fields to be returned
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@param conds WHERE clause
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@note
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This function is only called for queries with aggregate functions and no
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GROUP BY part. This means that the result set shall contain a single
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row only
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@retval
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0 no errors
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@retval
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1 if all items were resolved
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@retval
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HA_ERR_KEY_NOT_FOUND on impossible conditions
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@retval
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HA_ERR_... if a deadlock or a lock wait timeout happens, for example
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@retval
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ER_... e.g. ER_SUBQUERY_NO_1_ROW
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*/
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int opt_sum_query(THD *thd,
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List<TABLE_LIST> &tables, List<Item> &all_fields, COND *conds)
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{
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List_iterator_fast<Item> it(all_fields);
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List_iterator<TABLE_LIST> ti(tables);
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TABLE_LIST *tl;
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int const_result= 1;
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bool recalc_const_item= 0;
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ulonglong count= 1;
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bool is_exact_count= TRUE, maybe_exact_count= TRUE;
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table_map removed_tables= 0, outer_tables= 0, used_tables= 0;
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table_map where_tables= 0;
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Item *item;
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int error= 0;
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DBUG_ENTER("opt_sum_query");
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if (conds)
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where_tables= conds->used_tables();
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/*
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Analyze outer join dependencies, and, if possible, compute the number
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of returned rows.
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*/
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while ((tl= ti++))
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{
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TABLE_LIST *embedded;
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for (embedded= tl ; embedded; embedded= embedded->embedding)
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{
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if (embedded->on_expr)
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break;
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}
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if (embedded)
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/* Don't replace expression on a table that is part of an outer join */
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{
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outer_tables|= tl->table->map;
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/*
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We can't optimise LEFT JOIN in cases where the WHERE condition
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restricts the table that is used, like in:
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SELECT MAX(t1.a) FROM t1 LEFT JOIN t2 join-condition
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WHERE t2.field IS NULL;
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*/
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if (tl->table->map & where_tables)
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DBUG_RETURN(0);
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}
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else
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used_tables|= tl->table->map;
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/*
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If the storage manager of 'tl' gives exact row count as part of
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statistics (cheap), compute the total number of rows. If there are
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no outer table dependencies, this count may be used as the real count.
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Schema tables are filled after this function is invoked, so we can't
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get row count
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*/
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if (!(tl->table->file->ha_table_flags() & HA_STATS_RECORDS_IS_EXACT) ||
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tl->schema_table)
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{
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maybe_exact_count&= test(!tl->schema_table &&
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(tl->table->file->ha_table_flags() &
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HA_HAS_RECORDS));
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is_exact_count= FALSE;
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count= 1; // ensure count != 0
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}
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else if (tl->is_materialized_derived() ||
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tl->jtbm_subselect)
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{
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/*
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Can't remove a derived table as it's number of rows is just an
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estimate.
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*/
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DBUG_RETURN(0);
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}
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else
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{
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error= tl->table->file->info(HA_STATUS_VARIABLE | HA_STATUS_NO_LOCK);
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if(error)
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{
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tl->table->file->print_error(error, MYF(0));
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tl->table->in_use->fatal_error();
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DBUG_RETURN(error);
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}
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count*= tl->table->file->stats.records;
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}
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}
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/*
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Iterate through all items in the SELECT clause and replace
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COUNT(), MIN() and MAX() with constants (if possible).
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*/
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while ((item= it++))
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{
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if (item->type() == Item::SUM_FUNC_ITEM)
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{
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Item_sum *item_sum= (((Item_sum*) item));
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switch (item_sum->sum_func()) {
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case Item_sum::COUNT_FUNC:
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/*
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If the expr in COUNT(expr) can never be null we can change this
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to the number of rows in the tables if this number is exact and
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there are no outer joins.
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*/
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if (!conds && !((Item_sum_count*) item)->get_arg(0)->maybe_null &&
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!outer_tables && maybe_exact_count)
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{
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if (!is_exact_count)
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{
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if ((count= get_exact_record_count(tables)) == ULONGLONG_MAX)
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{
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/* Error from handler in counting rows. Don't optimize count() */
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const_result= 0;
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continue;
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}
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is_exact_count= 1; // count is now exact
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}
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((Item_sum_count*) item)->make_const((longlong) count);
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recalc_const_item= 1;
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}
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else
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const_result= 0;
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break;
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case Item_sum::MIN_FUNC:
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case Item_sum::MAX_FUNC:
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{
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int is_max= test(item_sum->sum_func() == Item_sum::MAX_FUNC);
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/*
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If MIN/MAX(expr) is the first part of a key or if all previous
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parts of the key is found in the COND, then we can use
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indexes to find the key.
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*/
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Item *expr=item_sum->get_arg(0);
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if (expr->real_item()->type() == Item::FIELD_ITEM)
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{
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uchar key_buff[MAX_KEY_LENGTH];
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TABLE_REF ref;
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uint range_fl, prefix_len;
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ref.key_buff= key_buff;
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Item_field *item_field= (Item_field*) (expr->real_item());
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TABLE *table= item_field->field->table;
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/*
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Look for a partial key that can be used for optimization.
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If we succeed, ref.key_length will contain the length of
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this key, while prefix_len will contain the length of
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the beginning of this key without field used in MIN/MAX().
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Type of range for the key part for this field will be
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returned in range_fl.
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*/
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if (table->file->inited || (outer_tables & table->map) ||
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!find_key_for_maxmin(is_max, &ref, item_field->field, conds,
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&range_fl, &prefix_len))
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{
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const_result= 0;
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break;
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}
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if (!(error= table->file->ha_index_init((uint) ref.key, 1)))
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error= (is_max ?
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get_index_max_value(table, &ref, range_fl) :
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get_index_min_value(table, &ref, item_field, range_fl,
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prefix_len));
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/* Verify that the read tuple indeed matches the search key */
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if (!error && reckey_in_range(is_max, &ref, item_field->field,
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conds, range_fl, prefix_len))
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error= HA_ERR_KEY_NOT_FOUND;
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table->disable_keyread();
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table->file->ha_index_end();
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if (error)
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{
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if (error == HA_ERR_KEY_NOT_FOUND || error == HA_ERR_END_OF_FILE)
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DBUG_RETURN(HA_ERR_KEY_NOT_FOUND); // No rows matching WHERE
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/* HA_ERR_LOCK_DEADLOCK or some other error */
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table->file->print_error(error, MYF(0));
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DBUG_RETURN(error);
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}
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removed_tables|= table->map;
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}
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else if (!expr->const_item() || !is_exact_count)
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{
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/*
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The optimization is not applicable in both cases:
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(a) 'expr' is a non-constant expression. Then we can't
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replace 'expr' by a constant.
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(b) 'expr' is a costant. According to ANSI, MIN/MAX must return
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NULL if the query does not return any rows. Thus, if we are not
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able to determine if the query returns any rows, we can't apply
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the optimization and replace MIN/MAX with a constant.
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*/
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const_result= 0;
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break;
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}
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/*
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If count == 0 (so is_exact_count == TRUE) and
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there're no outer joins, set to NULL,
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otherwise set to the constant value.
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*/
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if (!count && !outer_tables)
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item_sum->clear();
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else
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item_sum->reset();
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item_sum->make_const();
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recalc_const_item= 1;
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break;
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}
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default:
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const_result= 0;
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break;
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}
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}
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else if (const_result)
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{
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if (recalc_const_item)
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item->update_used_tables();
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if (!item->const_item())
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const_result= 0;
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}
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}
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if (thd->is_error())
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DBUG_RETURN(thd->main_da.sql_errno());
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/*
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If we have a where clause, we can only ignore searching in the
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tables if MIN/MAX optimisation replaced all used tables
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We do not use replaced values in case of:
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SELECT MIN(key) FROM table_1, empty_table
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removed_tables is != 0 if we have used MIN() or MAX().
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*/
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if (removed_tables && used_tables != removed_tables)
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const_result= 0; // We didn't remove all tables
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DBUG_RETURN(const_result);
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}
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|
|
|
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/**
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Test if the predicate compares a field with constants.
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|
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@param func_item Predicate item
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@param[out] args Here we store the field followed by constants
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@param[out] inv_order Is set to 1 if the predicate is of the form
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'const op field'
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@retval
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0 func_item is a simple predicate: a field is compared with
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constants
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@retval
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1 Otherwise
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*/
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bool simple_pred(Item_func *func_item, Item **args, bool *inv_order)
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{
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Item *item;
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*inv_order= 0;
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switch (func_item->argument_count()) {
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case 0:
|
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/* MULT_EQUAL_FUNC */
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{
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Item_equal *item_equal= (Item_equal *) func_item;
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if (!(args[1]= item_equal->get_const()))
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return 0;
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Item_equal_fields_iterator it(*item_equal);
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if (!(item= it++))
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return 0;
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args[0]= item->real_item();
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if (it++)
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return 0;
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}
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break;
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case 1:
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/* field IS NULL */
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item= func_item->arguments()[0]->real_item();
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if (item->type() != Item::FIELD_ITEM)
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return 0;
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args[0]= item;
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break;
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case 2:
|
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/* 'field op const' or 'const op field' */
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item= func_item->arguments()[0]->real_item();
|
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if (item->type() == Item::FIELD_ITEM)
|
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{
|
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args[0]= item;
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item= func_item->arguments()[1]->real_item();
|
|
if (!item->const_item())
|
|
return 0;
|
|
args[1]= item;
|
|
}
|
|
else if (item->const_item())
|
|
{
|
|
args[1]= item;
|
|
item= func_item->arguments()[1]->real_item();
|
|
if (item->type() != Item::FIELD_ITEM)
|
|
return 0;
|
|
args[0]= item;
|
|
*inv_order= 1;
|
|
}
|
|
else
|
|
return 0;
|
|
break;
|
|
case 3:
|
|
/* field BETWEEN const AND const */
|
|
item= func_item->arguments()[0]->real_item();
|
|
if (item->type() == Item::FIELD_ITEM)
|
|
{
|
|
args[0]= item;
|
|
for (int i= 1 ; i <= 2; i++)
|
|
{
|
|
item= func_item->arguments()[i]->real_item();
|
|
if (!item->const_item())
|
|
return 0;
|
|
args[i]= item;
|
|
}
|
|
}
|
|
else
|
|
return 0;
|
|
}
|
|
return 1;
|
|
}
|
|
|
|
|
|
/**
|
|
Check whether a condition matches a key to get {MAX|MIN}(field):.
|
|
|
|
For the index specified by the keyinfo parameter and an index that
|
|
contains the field as its component (field_part), the function
|
|
checks whether
|
|
|
|
- the condition cond is a conjunction,
|
|
- all of its conjuncts refer to columns of the same table, and
|
|
- each conjunct is on one of the following forms:
|
|
- f_i = const_i or const_i = f_i or f_i IS NULL,
|
|
where f_i is part of the index
|
|
- field {<|<=|>=|>|=} const
|
|
- const {<|<=|>=|>|=} field
|
|
- field BETWEEN const_1 AND const_2
|
|
|
|
As a side-effect, the key value to be used for looking up the MIN/MAX value
|
|
is actually stored inside the Field object. An interesting feature is that
|
|
the function will find the most restrictive endpoint by over-eager
|
|
evaluation of the @c WHERE condition. It continually stores the current
|
|
endpoint inside the Field object. For a query such as
|
|
|
|
@code
|
|
SELECT MIN(a) FROM t1 WHERE a > 3 AND a > 5;
|
|
@endcode
|
|
|
|
the algorithm will recurse over the conjuction, storing first a 3 in the
|
|
field. In the next recursive invocation the expression a > 5 is evaluated
|
|
as 3 > 5 (Due to the dual nature of Field objects as value carriers and
|
|
field identifiers), which will obviously fail, leading to 5 being stored in
|
|
the Field object.
|
|
|
|
@param[in] max_fl Set to true if we are optimizing MAX(),
|
|
false means we are optimizing %MIN()
|
|
@param[in, out] ref Reference to the structure where the function
|
|
stores the key value
|
|
@param[in] keyinfo Reference to the key info
|
|
@param[in] field_part Pointer to the key part for the field
|
|
@param[in] cond WHERE condition
|
|
@param[in,out] key_part_used Map of matchings parts. The function will output
|
|
the set of key parts actually being matched in
|
|
this set, yet it relies on the caller to
|
|
initialize the value to zero. This is due
|
|
to the fact that this value is passed
|
|
recursively.
|
|
@param[in,out] range_fl Says whether endpoints use strict greater/less
|
|
than.
|
|
@param[out] prefix_len Length of common key part for the range
|
|
where MAX/MIN is searched for
|
|
|
|
@retval
|
|
false Index can't be used.
|
|
@retval
|
|
true We can use the index to get MIN/MAX value
|
|
*/
|
|
|
|
static bool matching_cond(bool max_fl, TABLE_REF *ref, KEY *keyinfo,
|
|
KEY_PART_INFO *field_part, COND *cond,
|
|
key_part_map *key_part_used, uint *range_fl,
|
|
uint *prefix_len)
|
|
{
|
|
DBUG_ENTER("matching_cond");
|
|
if (!cond)
|
|
DBUG_RETURN(TRUE);
|
|
Field *field= field_part->field;
|
|
if (cond->used_tables() & OUTER_REF_TABLE_BIT)
|
|
{
|
|
DBUG_RETURN(FALSE);
|
|
}
|
|
if (!(cond->used_tables() & field->table->map) &&
|
|
test(cond->used_tables() & ~PSEUDO_TABLE_BITS))
|
|
{
|
|
/* Condition doesn't restrict the used table */
|
|
DBUG_RETURN(!cond->const_item());
|
|
}
|
|
else if (cond->is_expensive())
|
|
DBUG_RETURN(FALSE);
|
|
if (cond->type() == Item::COND_ITEM)
|
|
{
|
|
if (((Item_cond*) cond)->functype() == Item_func::COND_OR_FUNC)
|
|
DBUG_RETURN(FALSE);
|
|
|
|
/* AND */
|
|
List_iterator_fast<Item> li(*((Item_cond*) cond)->argument_list());
|
|
Item *item;
|
|
while ((item= li++))
|
|
{
|
|
if (!matching_cond(max_fl, ref, keyinfo, field_part, item,
|
|
key_part_used, range_fl, prefix_len))
|
|
DBUG_RETURN(FALSE);
|
|
}
|
|
DBUG_RETURN(TRUE);
|
|
}
|
|
|
|
if (cond->type() != Item::FUNC_ITEM)
|
|
DBUG_RETURN(FALSE); // Not operator, can't optimize
|
|
|
|
bool eq_type= 0; // =, <=> or IS NULL
|
|
bool is_null_safe_eq= FALSE; // The operator is NULL safe, e.g. <=>
|
|
bool noeq_type= 0; // < or >
|
|
bool less_fl= 0; // < or <=
|
|
bool is_null= 0; // IS NULL
|
|
bool between= 0; // BETWEEN ... AND ...
|
|
|
|
switch (((Item_func*) cond)->functype()) {
|
|
case Item_func::ISNULL_FUNC:
|
|
is_null= 1; /* fall through */
|
|
case Item_func::EQ_FUNC:
|
|
eq_type= TRUE;
|
|
break;
|
|
case Item_func::EQUAL_FUNC:
|
|
eq_type= is_null_safe_eq= TRUE;
|
|
break;
|
|
case Item_func::LT_FUNC:
|
|
noeq_type= 1; /* fall through */
|
|
case Item_func::LE_FUNC:
|
|
less_fl= 1;
|
|
break;
|
|
case Item_func::GT_FUNC:
|
|
noeq_type= 1; /* fall through */
|
|
case Item_func::GE_FUNC:
|
|
break;
|
|
case Item_func::BETWEEN:
|
|
if (((Item_func_between*) cond)->negated)
|
|
DBUG_RETURN(FALSE);
|
|
between= 1;
|
|
break;
|
|
case Item_func::MULT_EQUAL_FUNC:
|
|
eq_type= 1;
|
|
break;
|
|
default:
|
|
DBUG_RETURN(FALSE); // Can't optimize function
|
|
}
|
|
|
|
Item *args[3];
|
|
bool inv;
|
|
|
|
/* Test if this is a comparison of a field and constant */
|
|
if (!simple_pred((Item_func*) cond, args, &inv))
|
|
DBUG_RETURN(FALSE);
|
|
|
|
if (!is_null_safe_eq && !is_null &&
|
|
(args[1]->is_null() || (between && args[2]->is_null())))
|
|
DBUG_RETURN(FALSE);
|
|
|
|
if (inv && !eq_type)
|
|
less_fl= 1-less_fl; // Convert '<' -> '>' (etc)
|
|
|
|
/* Check if field is part of the tested partial key */
|
|
uchar *key_ptr= ref->key_buff;
|
|
KEY_PART_INFO *part;
|
|
for (part= keyinfo->key_part; ; key_ptr+= part++->store_length)
|
|
|
|
{
|
|
if (part > field_part)
|
|
DBUG_RETURN(FALSE); // Field is beyond the tested parts
|
|
if (part->field->eq(((Item_field*) args[0])->field))
|
|
break; // Found a part of the key for the field
|
|
}
|
|
|
|
bool is_field_part= part == field_part;
|
|
if (!(is_field_part || eq_type))
|
|
DBUG_RETURN(FALSE);
|
|
|
|
key_part_map org_key_part_used= *key_part_used;
|
|
if (eq_type || between || max_fl == less_fl)
|
|
{
|
|
uint length= (key_ptr-ref->key_buff)+part->store_length;
|
|
if (ref->key_length < length)
|
|
{
|
|
/* Ultimately ref->key_length will contain the length of the search key */
|
|
ref->key_length= length;
|
|
ref->key_parts= (part - keyinfo->key_part) + 1;
|
|
}
|
|
if (!*prefix_len && part+1 == field_part)
|
|
*prefix_len= length;
|
|
if (is_field_part && eq_type)
|
|
*prefix_len= ref->key_length;
|
|
|
|
*key_part_used|= (key_part_map) 1 << (part - keyinfo->key_part);
|
|
}
|
|
|
|
if (org_key_part_used == *key_part_used &&
|
|
/*
|
|
The current search key is not being extended with a new key part. This
|
|
means that the a condition is added a key part for which there was a
|
|
previous condition. We can only overwrite such key parts in some special
|
|
cases, e.g. a > 2 AND a > 1 (here range_fl must be set to something). In
|
|
all other cases the WHERE condition is always false anyway.
|
|
*/
|
|
(eq_type || *range_fl == 0))
|
|
DBUG_RETURN(FALSE);
|
|
|
|
if (org_key_part_used != *key_part_used ||
|
|
(is_field_part &&
|
|
(between || eq_type || max_fl == less_fl) && !cond->val_int()))
|
|
{
|
|
/*
|
|
It's the first predicate for this part or a predicate of the
|
|
following form that moves upper/lower bounds for max/min values:
|
|
- field BETWEEN const AND const
|
|
- field = const
|
|
- field {<|<=} const, when searching for MAX
|
|
- field {>|>=} const, when searching for MIN
|
|
*/
|
|
|
|
if (is_null || (is_null_safe_eq && args[1]->is_null()))
|
|
{
|
|
/*
|
|
If we have a non-nullable index, we cannot use it,
|
|
since set_null will be ignored, and we will compare uninitialized data.
|
|
*/
|
|
if (!part->field->real_maybe_null())
|
|
DBUG_RETURN(FALSE);
|
|
part->field->set_null();
|
|
*key_ptr= (uchar) 1;
|
|
}
|
|
else
|
|
{
|
|
/* Update endpoints for MAX/MIN, see function comment. */
|
|
Item *value= args[between && max_fl ? 2 : 1];
|
|
store_val_in_field(part->field, value, CHECK_FIELD_IGNORE);
|
|
if (part->null_bit)
|
|
*key_ptr++= (uchar) test(part->field->is_null());
|
|
part->field->get_key_image(key_ptr, part->length, Field::itRAW);
|
|
}
|
|
if (is_field_part)
|
|
{
|
|
if (between || eq_type)
|
|
*range_fl&= ~(NO_MAX_RANGE | NO_MIN_RANGE);
|
|
else
|
|
{
|
|
*range_fl&= ~(max_fl ? NO_MAX_RANGE : NO_MIN_RANGE);
|
|
if (noeq_type)
|
|
*range_fl|= (max_fl ? NEAR_MAX : NEAR_MIN);
|
|
else
|
|
*range_fl&= ~(max_fl ? NEAR_MAX : NEAR_MIN);
|
|
}
|
|
}
|
|
}
|
|
else if (eq_type)
|
|
{
|
|
if ((!is_null && !cond->val_int()) ||
|
|
(is_null && !test(part->field->is_null())))
|
|
DBUG_RETURN(FALSE); // Impossible test
|
|
}
|
|
else if (is_field_part)
|
|
*range_fl&= ~(max_fl ? NO_MIN_RANGE : NO_MAX_RANGE);
|
|
DBUG_RETURN(TRUE);
|
|
}
|
|
|
|
|
|
/**
|
|
Check whether we can get value for {max|min}(field) by using a key.
|
|
|
|
If where-condition is not a conjunction of 0 or more conjuct the
|
|
function returns false, otherwise it checks whether there is an
|
|
index including field as its k-th component/part such that:
|
|
|
|
-# for each previous component f_i there is one and only one conjunct
|
|
of the form: f_i= const_i or const_i= f_i or f_i is null
|
|
-# references to field occur only in conjucts of the form:
|
|
field {<|<=|>=|>|=} const or const {<|<=|>=|>|=} field or
|
|
field BETWEEN const1 AND const2
|
|
-# all references to the columns from the same table as column field
|
|
occur only in conjucts mentioned above.
|
|
-# each of k first components the index is not partial, i.e. is not
|
|
defined on a fixed length proper prefix of the field.
|
|
|
|
If such an index exists the function through the ref parameter
|
|
returns the key value to find max/min for the field using the index,
|
|
the length of first (k-1) components of the key and flags saying
|
|
how to apply the key for the search max/min value.
|
|
(if we have a condition field = const, prefix_len contains the length
|
|
of the whole search key)
|
|
|
|
@param[in] max_fl 0 for MIN(field) / 1 for MAX(field)
|
|
@param[in,out] ref Reference to the structure we store the key value
|
|
@param[in] field Field used inside MIN() / MAX()
|
|
@param[in] cond WHERE condition
|
|
@param[out] range_fl Bit flags for how to search if key is ok
|
|
@param[out] prefix_len Length of prefix for the search range
|
|
|
|
@note
|
|
This function may set field->table->key_read to true,
|
|
which must be reset after index is used!
|
|
(This can only happen when function returns 1)
|
|
|
|
@retval
|
|
0 Index can not be used to optimize MIN(field)/MAX(field)
|
|
@retval
|
|
1 Can use key to optimize MIN()/MAX().
|
|
In this case ref, range_fl and prefix_len are updated
|
|
*/
|
|
|
|
|
|
static bool find_key_for_maxmin(bool max_fl, TABLE_REF *ref,
|
|
Field* field, COND *cond,
|
|
uint *range_fl, uint *prefix_len)
|
|
{
|
|
if (!(field->flags & PART_KEY_FLAG))
|
|
return FALSE; // Not key field
|
|
|
|
DBUG_ENTER("find_key_for_maxmin");
|
|
|
|
TABLE *table= field->table;
|
|
uint idx= 0;
|
|
|
|
KEY *keyinfo,*keyinfo_end;
|
|
for (keyinfo= table->key_info, keyinfo_end= keyinfo+table->s->keys ;
|
|
keyinfo != keyinfo_end;
|
|
keyinfo++,idx++)
|
|
{
|
|
KEY_PART_INFO *part,*part_end;
|
|
key_part_map key_part_to_use= 0;
|
|
/*
|
|
Perform a check if index is not disabled by ALTER TABLE
|
|
or IGNORE INDEX.
|
|
*/
|
|
if (!table->keys_in_use_for_query.is_set(idx))
|
|
continue;
|
|
uint jdx= 0;
|
|
*prefix_len= 0;
|
|
for (part= keyinfo->key_part, part_end= part+keyinfo->key_parts ;
|
|
part != part_end ;
|
|
part++, jdx++, key_part_to_use= (key_part_to_use << 1) | 1)
|
|
{
|
|
if (!(table->file->index_flags(idx, jdx, 0) & HA_READ_ORDER))
|
|
DBUG_RETURN(FALSE);
|
|
|
|
/* Check whether the index component is partial */
|
|
Field *part_field= table->field[part->fieldnr-1];
|
|
if ((part_field->flags & BLOB_FLAG) ||
|
|
part->length < part_field->key_length())
|
|
break;
|
|
|
|
if (field->eq(part->field))
|
|
{
|
|
ref->key= idx;
|
|
ref->key_length= 0;
|
|
ref->key_parts= 0;
|
|
key_part_map key_part_used= 0;
|
|
*range_fl= NO_MIN_RANGE | NO_MAX_RANGE;
|
|
if (matching_cond(max_fl, ref, keyinfo, part, cond,
|
|
&key_part_used, range_fl, prefix_len) &&
|
|
!(key_part_to_use & ~key_part_used))
|
|
{
|
|
if (!max_fl && key_part_used == key_part_to_use && part->null_bit)
|
|
{
|
|
/*
|
|
The query is on this form:
|
|
|
|
SELECT MIN(key_part_k)
|
|
FROM t1
|
|
WHERE key_part_1 = const and ... and key_part_k-1 = const
|
|
|
|
If key_part_k is nullable, we want to find the first matching row
|
|
where key_part_k is not null. The key buffer is now {const, ...,
|
|
NULL}. This will be passed to the handler along with a flag
|
|
indicating open interval. If a tuple is read that does not match
|
|
these search criteria, an attempt will be made to read an exact
|
|
match for the key buffer.
|
|
*/
|
|
/* Set the first byte of key_part_k to 1, that means NULL */
|
|
ref->key_buff[ref->key_length]= 1;
|
|
ref->key_length+= part->store_length;
|
|
ref->key_parts++;
|
|
DBUG_ASSERT(ref->key_parts == jdx+1);
|
|
*range_fl&= ~NO_MIN_RANGE;
|
|
*range_fl|= NEAR_MIN; // Open interval
|
|
}
|
|
/*
|
|
The following test is false when the key in the key tree is
|
|
converted (for example to upper case)
|
|
*/
|
|
if (field->part_of_key.is_set(idx))
|
|
table->enable_keyread();
|
|
DBUG_RETURN(TRUE);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
DBUG_RETURN(FALSE);
|
|
}
|
|
|
|
|
|
/**
|
|
Check whether found key is in range specified by conditions.
|
|
|
|
@param[in] max_fl 0 for MIN(field) / 1 for MAX(field)
|
|
@param[in] ref Reference to the key value and info
|
|
@param[in] field Field used the MIN/MAX expression
|
|
@param[in] cond WHERE condition
|
|
@param[in] range_fl Says whether there is a condition to to be checked
|
|
@param[in] prefix_len Length of the constant part of the key
|
|
|
|
@retval
|
|
0 ok
|
|
@retval
|
|
1 WHERE was not true for the found row
|
|
*/
|
|
|
|
static int reckey_in_range(bool max_fl, TABLE_REF *ref, Field* field,
|
|
COND *cond, uint range_fl, uint prefix_len)
|
|
{
|
|
if (key_cmp_if_same(field->table, ref->key_buff, ref->key, prefix_len))
|
|
return 1;
|
|
if (!cond || (range_fl & (max_fl ? NO_MIN_RANGE : NO_MAX_RANGE)))
|
|
return 0;
|
|
return maxmin_in_range(max_fl, field, cond);
|
|
}
|
|
|
|
|
|
/**
|
|
Check whether {MAX|MIN}(field) is in range specified by conditions.
|
|
|
|
@param[in] max_fl 0 for MIN(field) / 1 for MAX(field)
|
|
@param[in] field Field used the MIN/MAX expression
|
|
@param[in] cond WHERE condition
|
|
|
|
@retval
|
|
0 ok
|
|
@retval
|
|
1 WHERE was not true for the found row
|
|
*/
|
|
|
|
static int maxmin_in_range(bool max_fl, Field* field, COND *cond)
|
|
{
|
|
/* If AND/OR condition */
|
|
if (cond->type() == Item::COND_ITEM)
|
|
{
|
|
List_iterator_fast<Item> li(*((Item_cond*) cond)->argument_list());
|
|
Item *item;
|
|
while ((item= li++))
|
|
{
|
|
if (maxmin_in_range(max_fl, field, item))
|
|
return 1;
|
|
}
|
|
return 0;
|
|
}
|
|
|
|
if (cond->used_tables() != field->table->map)
|
|
return 0;
|
|
bool less_fl= 0;
|
|
switch (((Item_func*) cond)->functype()) {
|
|
case Item_func::BETWEEN:
|
|
return cond->val_int() == 0; // Return 1 if WHERE is false
|
|
case Item_func::LT_FUNC:
|
|
case Item_func::LE_FUNC:
|
|
less_fl= 1;
|
|
case Item_func::GT_FUNC:
|
|
case Item_func::GE_FUNC:
|
|
{
|
|
Item *item= ((Item_func*) cond)->arguments()[1];
|
|
/* In case of 'const op item' we have to swap the operator */
|
|
if (!item->const_item())
|
|
less_fl= 1-less_fl;
|
|
/*
|
|
We only have to check the expression if we are using an expression like
|
|
SELECT MAX(b) FROM t1 WHERE a=const AND b>const
|
|
not for
|
|
SELECT MAX(b) FROM t1 WHERE a=const AND b<const
|
|
*/
|
|
if (max_fl != less_fl)
|
|
return cond->val_int() == 0; // Return 1 if WHERE is false
|
|
return 0;
|
|
}
|
|
default:
|
|
break; // Ignore
|
|
}
|
|
return 0;
|
|
}
|
|
|