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Bug#17217128 : BAD INTERACTION BETWEEN MIN/MAX AND

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"HAVING SUM(DISTINCT)": WRONG RESULTS.
ISSUE:
------
If a query uses loose index scan and it has both
AGG(DISTINCT) and MIN()/MAX()functions. Then, result values
of MIN/MAX() is set improperly.
When query has AGG(DISTINCT) then end_select is set to
end_send_group. "end_send_group" keeps doing aggregation
until it sees a record from next group. And, then it will
send out the result row of that group.
Since query also has MIN()/MAX() and loose index scan is
used, values of MIN/MAX() are set as part of loose index
scan itself. Setting MIN()/MAX() values as part of loose
index scan overwrites values computed in end_send_group.
This caused invalid result.
For such queries to work loose index scan should stop
performing MIN/MAX() aggregation. And, let end_send_group to
do the same. But according to current design loose index
scan can produce only one row per group key. If we have both
MIN() and MAX() then it has to give two records out. This is
not possible as interface has to use common buffer
record[0]! for both records at a time.

SOLUTIONS:
----------
For such queries to work we need a new interface for loose
index scan. Hence, do not choose loose_index_scan for such
cases. So a new rule SA7 is introduced to take care of the
same.

SA7: "If Q has both AGG_FUNC(DISTINCT ...) and
      MIN/MAX() functions then loose index scan access
      method is not used."
This commit is contained in:
mithun 2014-05-15 11:46:57 +05:30
parent 5228395a31
commit 4c4def9043
3 changed files with 95 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

56
mysql-test/r/group_min_max.result
View File

@ -3001,7 +3001,7 @@ COUNT(DISTINCT a, b) SUM(DISTINCT a)
0 NULL
EXPLAIN SELECT SUM(DISTINCT a), MAX(b) FROM t2 GROUP BY a;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t2 range NULL a 5 NULL 9 Using index for group-by
1 SIMPLE t2 index NULL a 15 NULL 16 Using index
SELECT SUM(DISTINCT a), MAX(b) FROM t2 GROUP BY a;
SUM(DISTINCT a) MAX(b)
1 8
@ -3029,7 +3029,7 @@ SELECT 42 * (a + c + COUNT(DISTINCT c, a, b)) FROM t2 GROUP BY a, b, c;
168
EXPLAIN SELECT (SUM(DISTINCT a) + MAX(b)) FROM t2 GROUP BY a;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t2 range NULL a 5 NULL 9 Using index for group-by
1 SIMPLE t2 index NULL a 15 NULL 16 Using index
SELECT (SUM(DISTINCT a) + MAX(b)) FROM t2 GROUP BY a;
(SUM(DISTINCT a) + MAX(b))
9
@ -3057,3 +3057,55 @@ id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 range NULL PRIMARY 5 NULL 9 Using index for group-by (scanning)
drop table t1;
# End of test#50539.
#
# Bug#17217128 - BAD INTERACTION BETWEEN MIN/MAX AND
# "HAVING SUM(DISTINCT)": WRONG RESULTS.
#
CREATE TABLE t (a INT, b INT, KEY(a,b));
INSERT INTO t VALUES (1,1), (2,2), (3,3), (4,4), (1,0), (3,2), (4,5);
ANALYZE TABLE t;
Table Op Msg_type Msg_text
test.t analyze status OK
SELECT a, SUM(DISTINCT a), MIN(b) FROM t GROUP BY a;
a SUM(DISTINCT a) MIN(b)
1 1 0
2 2 2
3 3 2
4 4 4
EXPLAIN SELECT a, SUM(DISTINCT a), MIN(b) FROM t GROUP BY a;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t index NULL a 10 NULL 7 Using index
SELECT a, SUM(DISTINCT a), MAX(b) FROM t GROUP BY a;
a SUM(DISTINCT a) MAX(b)
1 1 1
2 2 2
3 3 3
4 4 5
EXPLAIN SELECT a, SUM(DISTINCT a), MAX(b) FROM t GROUP BY a;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t index NULL a 10 NULL 7 Using index
SELECT a, MAX(b) FROM t GROUP BY a HAVING SUM(DISTINCT a);
a MAX(b)
1 1
2 2
3 3
4 5
EXPLAIN SELECT a, MAX(b) FROM t GROUP BY a HAVING SUM(DISTINCT a);
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t index NULL a 10 NULL 7 Using index
SELECT SUM(DISTINCT a), MIN(b), MAX(b) FROM t;
SUM(DISTINCT a) MIN(b) MAX(b)
10 0 5
EXPLAIN SELECT SUM(DISTINCT a), MIN(b), MAX(b) FROM t;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t index NULL a 10 NULL 7 Using index
SELECT a, SUM(DISTINCT a), MIN(b), MAX(b) FROM t GROUP BY a;
a SUM(DISTINCT a) MIN(b) MAX(b)
1 1 0 1
2 2 2 2
3 3 2 3
4 4 4 5
EXPLAIN SELECT a, SUM(DISTINCT a), MIN(b), MAX(b) FROM t GROUP BY a;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t index NULL a 10 NULL 7 Using index
DROP TABLE t;

24
mysql-test/t/group_min_max.test
View File

@ -1243,3 +1243,27 @@ explain SELECT f1, COUNT(DISTINCT f2) FROM t1 GROUP BY f1;
drop table t1;
--echo # End of test#50539.
--echo #
--echo # Bug#17217128 - BAD INTERACTION BETWEEN MIN/MAX AND
--echo # "HAVING SUM(DISTINCT)": WRONG RESULTS.
--echo #
CREATE TABLE t (a INT, b INT, KEY(a,b));
INSERT INTO t VALUES (1,1), (2,2), (3,3), (4,4), (1,0), (3,2), (4,5);
ANALYZE TABLE t;
SELECT a, SUM(DISTINCT a), MIN(b) FROM t GROUP BY a;
EXPLAIN SELECT a, SUM(DISTINCT a), MIN(b) FROM t GROUP BY a;
SELECT a, SUM(DISTINCT a), MAX(b) FROM t GROUP BY a;
EXPLAIN SELECT a, SUM(DISTINCT a), MAX(b) FROM t GROUP BY a;
SELECT a, MAX(b) FROM t GROUP BY a HAVING SUM(DISTINCT a);
EXPLAIN SELECT a, MAX(b) FROM t GROUP BY a HAVING SUM(DISTINCT a);
SELECT SUM(DISTINCT a), MIN(b), MAX(b) FROM t;
EXPLAIN SELECT SUM(DISTINCT a), MIN(b), MAX(b) FROM t;
SELECT a, SUM(DISTINCT a), MIN(b), MAX(b) FROM t GROUP BY a;
EXPLAIN SELECT a, SUM(DISTINCT a), MIN(b), MAX(b) FROM t GROUP BY a;
DROP TABLE t;

17
sql/opt_range.cc
View File

@ -9471,6 +9471,16 @@ cost_group_min_max(TABLE* table, KEY *index_info, uint used_key_parts,
never stored after a unique key lookup in the clustered index and
furhter index_next/prev calls can not be used. So loose index scan
optimization can not be used in this case.
SA7. If Q has both AGG_FUNC(DISTINCT ...) and MIN/MAX() functions then this
access method is not used.
For above queries MIN/MAX() aggregation has to be done at
nested_loops_join (end_send_group). But with current design MIN/MAX()
is always set as part of loose index scan. Because of this mismatch
MIN() and MAX() values will be set incorrectly. For such queries to
work we need a new interface for loose index scan. This new interface
should only fetch records with min and max values and let
end_send_group to do aggregation. Until then do not use
loose_index_scan.
GA1. If Q has a GROUP BY clause, then GA is a prefix of I. That is, if
G_i = A_j => i = j.
GA2. If Q has a DISTINCT clause, then there is a permutation of SA that
@ -9636,6 +9646,13 @@ get_best_group_min_max(PARAM *param, SEL_TREE *tree, double read_time)
DBUG_RETURN(NULL);
}
}
/* Check (SA7). */
if (is_agg_distinct && (have_max || have_min))
{
DBUG_RETURN(NULL);
}
/* Check (SA5). */
if (join->select_distinct)
{