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count(distinct) cleanup

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sasha@mysql.sashanet.com 2001-05-29 18:53:37 -06:00
parent 73e6a69052
commit 6ecaac01f0
3 changed files with 13 additions and 6 deletions
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2
mysql-test/t/count_distinct2.test
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@ -45,7 +45,7 @@ select count(distinct n2), n1 from t1 group by n1;
drop table t1;
# test the converstion from tree to MyISAM
create table t1 (n int);
create table t1 (n int default NULL);
let $1=5000;
while ($1)
{

10
sql/item_sum.cc
View file

@ -839,7 +839,8 @@ int dump_leaf(byte* key, uint32 count __attribute__((unused)),
{
char* buf = item->table->record[0];
int error;
memset(buf, 0xff, item->rec_offset); // make up for cheating in the tree
// the first item->rec_offset bytes are taken care of with
// restore_record(table,2) in setup()
memcpy(buf + item->rec_offset, key, item->tree.size_of_element);
if ((error = item->table->file->write_row(buf)))
{
@ -888,12 +889,17 @@ bool Item_sum_count_distinct::setup(THD *thd)
table->file->extra(HA_EXTRA_NO_ROWS); // Don't update rows
table->no_rows=1;
if(table->db_type == DB_TYPE_HEAP) // no blobs, otherwise it would be
// MyISAM
{
qsort_cmp2 compare_key;
void* cmp_arg;
int key_len;
// to make things easier for dump_leaf if we ever have to dump to
// MyISAM
restore_record(table,2);
if(table->fields == 1) // if we have only one field, which is
// the most common use of count(distinct), it is much faster
@ -941,7 +947,7 @@ bool Item_sum_count_distinct::setup(THD *thd)
// but this has to be handled - otherwise someone can crash
// the server with a DoS attack
max_elements_in_tree = (key_len) ? max_heap_table_size/key_len :
max_heap_table_size;
1;
}
return 0;

7
sql/item_sum.h
View file

@ -148,19 +148,20 @@ class Item_sum_count_distinct :public Item_sum_int
bool fix_fields(THD *thd,TABLE_LIST *tables);
TMP_TABLE_PARAM *tmp_table_param;
TREE tree;
uint max_elements_in_tree;
// calculated based on max_heap_table_size. If reached,
// walk the tree and dump it into MyISAM table
uint max_elements_in_tree;
bool use_tree;
// If there are no blobs, we can use a tree, which
// is faster than heap table. In that case, we still use the table
// to help get things set up, but we insert nothing in it
bool use_tree;
int rec_offset;
// the first few bytes of record ( at least one)
// are just markers for deleted and NULLs. We want to skip them since
// they will just bloat the tree without providing any valuable info
int rec_offset;
int tree_to_myisam();