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Bug#49771: Incorrect MIN/MAX for date/time values.

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This bug is a design flaw of the fix for the bug#33546. It assumed that an
item can be used only in one comparison context, but actually it isn't the
case. Item_cache_datetime is used to store result for MIX/MAX aggregate
functions. Because Arg_comparator always compares datetime values as INTs when
possible the Item_cache_datetime most time caches only INT value. But
since all datetime values has STRING result type MIN/MAX functions are asked
for a STRING value when the result is being sent to a client. The
Item_cache_datetime was designed to avoid conversions and get INT/STRING
values from an underlying item, but at the moment the values is asked
underlying item doesn't hold it anymore thus wrong result is returned.
Beside that MIN/MAX aggregate functions was wrongly initializing cached result
and this led to a wrong result.

The Item::has_compatible_context helper function is added. It checks whether
this and given items has the same comparison context or can be compared as
DATETIME values by Arg_comparator. The equality propagation optimization is
adjusted to take into account that items which being compared as DATETIME
can have different comparison contexts.
The Item_cache_datetime now converts cached INT value to a correct STRING
DATETIME value by means of number_to_datetime & my_TIME_to_str functions.
The Arg_comparator::set_cmp_context_for_datetime helper function is added. 
It sets comparison context of items being compared as DATETIMEs to INT if
items will be compared as longlong.
The Item_sum_hybrid::setup function now correctly initializes its result
value.
In order to avoid unnecessary conversions Item_sum_hybrid now states that it
can provide correct longlong value if the item being aggregated can do it
too.
This commit is contained in:
Evgeny Potemkin
2010-07-19 21:11:47 +04:00
parent 40856e830d
commit 589027b2f5
8 changed files with 169 additions and 32 deletions
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23
mysql-test/t/group_by.test
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@@ -1224,3 +1224,26 @@ DROP TABLE t1, t2;
--echo #
--echo # End of 5.1 tests
--echo #
--echo # Bug#49771: Incorrect MIN (date) when minimum value is 0000-00-00
--echo #
CREATE TABLE t1 (f1 int, f2 DATE);
INSERT INTO t1 VALUES (1,'2004-04-19'), (1,'0000-00-00'), (1,'2004-04-18'),
(2,'2004-05-19'), (2,'0001-01-01'), (3,'2004-04-10');
SELECT MIN(f2),MAX(f2) FROM t1;
SELECT f1,MIN(f2),MAX(f2) FROM t1 GROUP BY 1;
DROP TABLE t1;
CREATE TABLE t1 ( f1 int, f2 time);
INSERT INTO t1 VALUES (1,'01:27:35'), (1,'06:11:01'), (2,'19:53:05'),
(2,'21:44:25'), (3,'10:55:12'), (3,'05:45:11'), (4,'00:25:00');
SELECT MIN(f2),MAX(f2) FROM t1;
SELECT f1,MIN(f2),MAX(f2) FROM t1 GROUP BY 1;
DROP TABLE t1;
--echo #End of test#49771