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MDEV-23525 Wrong result of MIN(time_expr) and MAX(time_expr) with GROUP BY

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Problem:

When calculatung MIN() and MAX() in a query with GROUP BY, like this:

  SELECT MIN(time_expr), MAX(time_expr) FROM t1 GROUP BY i;

the code in Item_sum_min_max::update_field() erroneosly used
string format comparison, therefore '100:20:30' was considered as
smaller than '10:20:30'.

Fix:

1. Implementing low level "native" related methods in class Time:
     Time::Time(const Native &native)           - convert native to Time
     Time::to_native(Native *to, uint decimals) - convert Time to native

   The "native" binary representation for TIME is equal to
   the binary data format of Field_timef, which is used to
   store TIME when mysql56_temporal_format is ON (default).

2. Implementing Type_handler_time_common "native" related methods:

  Type_handler_time_common::cmp_native()
  Type_handler_time_common::Item_val_native_with_conversion()
  Type_handler_time_common::Item_val_native_with_conversion_result()
  Type_handler_time_common::Item_param_val_native()

3. Implementing missing "native representation" related methods
   in Field_time and Field_timef:

  Field_time::store_native()
  Field_time::val_native()
  Field_timef::store_native()
  Field_timef::val_native()

4. Implementing missing "native" related methods in all Items
   that can have the TIME data type:

  Item_timefunc::val_native()
  Item_name_const::val_native()
  Item_time_literal::val_native()
  Item_cache_time::val_native()
  Item_handled_func::val_native()

5. Marking Type_handler_time_common as "native ready".
   So now Item_sum_min_max::update_field() calculates
   values using min_max_update_native_field(),
   which uses native binary representation rather than string representation.

   Before this change, only the TIMESTAMP data type used native
   representation to calculate MIN() and MAX().

Benchmarks (see more details in MDEV):

  This change not only fixes the wrong result, but also
  makes a "SELECT .. MAX.. GROUP BY .." query faster:

  # TIME(0)
  CREATE TABLE t1 (id INT, time_col TIME) ENGINE=HEAP;
  INSERT INTO t1 VALUES (1,'10:10:10'); -- repeat this 1m times
  SELECT id, MAX(time_col) FROM t1 GROUP BY id;

  MySQL80: 0.159 sec
  10.3:    0.108 sec
  10.4:    0.094 sec (fixed)

  # TIME(6):
  CREATE TABLE t1 (id INT, time_col TIME(6)) ENGINE=HEAP;
  INSERT INTO t1 VALUES (1,'10:10:10.999999'); -- repeat this 1m times
  SELECT id, MAX(time_col) FROM t1 GROUP BY id;

  My80: 0.154
  10.3: 0.135
  10.4: 0.093 (fixed)
This commit is contained in:
Alexander Barkov
2020-08-21 19:41:51 +04:00
parent aa6cb7ed03
commit ae33ebe5b3
10 changed files with 364 additions and 4 deletions
Download Patch File Download Diff File Expand all files Collapse all files

9
sql/sql_type.h
View File

@ -1308,6 +1308,7 @@ class Schema;
*/
class Time: public Temporal
{
static uint binary_length_to_precision(uint length);
public:
enum datetime_to_time_mode_t
{
@ -1540,6 +1541,7 @@ public:
*/
Time(int *warn, bool neg, ulonglong hour, uint minute, const Sec6 &second);
Time() { time_type= MYSQL_TIMESTAMP_NONE; }
Time(const Native &native);
Time(Item *item)
:Time(current_thd, item)
{ }
@ -1695,6 +1697,7 @@ public:
return !is_valid_time() ? 0 :
Temporal::to_double(neg, TIME_to_ulonglong_time(this), second_part);
}
bool to_native(Native *to, uint decimals) const;
String *to_string(String *str, uint dec) const
{
if (!is_valid_time())
@ -5324,6 +5327,12 @@ public:
{
return MYSQL_TIMESTAMP_TIME;
}
bool is_val_native_ready() const { return true; }
const Type_handler *type_handler_for_native_format() const;
int cmp_native(const Native &a, const Native &b) const;
bool Item_val_native_with_conversion(THD *thd, Item *, Native *to) const;
bool Item_val_native_with_conversion_result(THD *thd, Item *, Native *to) const;
bool Item_param_val_native(THD *thd, Item_param *item, Native *to) const;
Item_literal *create_literal_item(THD *thd, const char *str, size_t length,
CHARSET_INFO *cs, bool send_error) const;
Item *create_typecast_item(THD *thd, Item *item,