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Fix for MIN/MAX with empty tables

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MIN(key_column) could in some cases return NULL on a column with NULL and other values.
MIN(key_column) and MAX(key_column) could in some cases return wrong values when used in OUTER JOIN.
This commit is contained in:
monty@mashka.mysql.fi
2003-02-03 20:20:32 +02:00
parent c42e94a6e6
commit e3cd63521c
8 changed files with 158 additions and 27 deletions
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92
sql/opt_sum.cc
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@ -1,4 +1,4 @@
/* Copyright (C) 2000 MySQL AB & MySQL Finland AB & TCX DataKonsult AB
/* Copyright (C) 2000-2003 MySQL AB
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
@ -22,28 +22,55 @@
static bool find_range_key(TABLE_REF *ref, Field* field,COND *cond);
/*****************************************************************************
** This function is only called for queries with sum functions and no
** GROUP BY part.
** This substitutes constants for some COUNT(), MIN() and MAX() functions.
** The function returns 1 if all items was resolved and -1 on impossible
** conditions
****************************************************************************/
/*
Substitutes constants for some COUNT(), MIN() and MAX() functions.
SYNOPSIS
opt_sum_query()
tables Tables in query
all_fields All fields to be returned
conds WHERE clause
NOTE:
This function is only called for queries with sum functions and no
GROUP BY part.
RETURN VALUES
0 No errors
1 if all items was resolved
-1 on impossible conditions
*/
int opt_sum_query(TABLE_LIST *tables, List<Item> &all_fields,COND *conds)
{
List_iterator_fast<Item> it(all_fields);
int const_result=1;
bool recalc_const_item=0;
table_map removed_tables=0;
int const_result= 1;
bool recalc_const_item= 0;
table_map removed_tables= 0, outer_tables= 0, used_tables= 0;
table_map where_tables= 0;
Item *item;
COND *org_conds= conds;
/* Add all ON conditions to WHERE condition */
if (conds)
where_tables= conds->used_tables();
/* Don't replace expression on a table that is part of an outer join */
for (TABLE_LIST *tl=tables; tl ; tl= tl->next)
{
if (tl->on_expr)
conds= and_expressions(conds, tl->on_expr, &org_conds);
{
outer_tables|= tl->table->map;
/*
We can't optimise LEFT JOIN in cases where the WHERE condition
restricts the table that is used, like in:
SELECT MAX(t1.a) FROM t1 LEFT JOIN t2 join-condition
WHERE t2.field IS NULL;
*/
if (tl->table->map & where_tables)
return 0;
}
used_tables|= tl->table->map;
}
/*
@ -68,8 +95,8 @@ int opt_sum_query(TABLE_LIST *tables, List<Item> &all_fields,COND *conds)
TABLE_LIST *table;
for (table=tables; table ; table=table->next)
{
if (table->on_expr || (table->table->file->table_flags() &
HA_NOT_EXACT_COUNT))
if (outer_tables || (table->table->file->table_flags() &
HA_NOT_EXACT_COUNT))
{
const_result=0; // Can't optimize left join
break;
@ -99,21 +126,35 @@ int opt_sum_query(TABLE_LIST *tables, List<Item> &all_fields,COND *conds)
byte key_buff[MAX_KEY_LENGTH];
TABLE_REF ref;
ref.key_buff=key_buff;
Item_field *item_field= ((Item_field*) expr);
TABLE *table= item_field->field->table;
if (!find_range_key(&ref, ((Item_field*) expr)->field,conds))
if ((outer_tables & table->map) ||
(!find_range_key(&ref, item_field->field,conds)))
{
const_result=0;
break;
}
TABLE *table=((Item_field*) expr)->field->table;
bool error=table->file->index_init((uint) ref.key);
bool error= table->file->index_init((uint) ref.key);
enum ha_rkey_function find_flag= HA_READ_KEY_OR_NEXT;
uint prefix_len= ref.key_length;
/*
If we are doing MIN() on a column with NULL fields
we must read the key after the NULL column
*/
if (item_field->field->null_bit)
{
ref.key_buff[ref.key_length++]=1;
find_flag= HA_READ_AFTER_KEY;
}
if (!ref.key_length)
error=table->file->index_first(table->record[0]) !=0;
else
error=table->file->index_read(table->record[0],key_buff,
ref.key_length,
HA_READ_KEY_OR_NEXT) ||
key_cmp(table, key_buff, ref.key, ref.key_length);
find_flag) ||
key_cmp(table, key_buff, ref.key, prefix_len);
if (table->key_read)
{
table->key_read=0;
@ -121,7 +162,7 @@ int opt_sum_query(TABLE_LIST *tables, List<Item> &all_fields,COND *conds)
}
table->file->index_end();
if (error)
return -1; // Impossible query
return -1; // No rows matching where
removed_tables|= table->map;
}
else if (!expr->const_item()) // This is VERY seldom false
@ -147,13 +188,14 @@ int opt_sum_query(TABLE_LIST *tables, List<Item> &all_fields,COND *conds)
byte key_buff[MAX_KEY_LENGTH];
TABLE_REF ref;
ref.key_buff=key_buff;
TABLE *table=((Item_field*) expr)->field->table;
if (!find_range_key(&ref, ((Item_field*) expr)->field,conds))
if ((outer_tables & table->map) ||
!find_range_key(&ref, ((Item_field*) expr)->field,conds))
{
const_result=0;
break;
}
TABLE *table=((Item_field*) expr)->field->table;
if ((table->file->table_flags() & HA_NOT_READ_AFTER_KEY))
{
const_result=0;
@ -203,8 +245,8 @@ int opt_sum_query(TABLE_LIST *tables, List<Item> &all_fields,COND *conds)
const_result=0;
}
}
if (conds && (conds->used_tables() & ~ removed_tables))
const_result=0;
if (used_tables != removed_tables)
const_result=0; // We didn't remove all tables
return const_result;
}