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Bug #30596 GROUP BY optimization gives wrong result order

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The optimization that uses a unique index to remove GROUP BY did not 
ensure that the index was actually used, thus violating the ORDER BY
that is implied by GROUP BY.
Fixed by replacing GROUP BY with ORDER BY if the GROUP BY clause contains
a unique index over non-nullable field(s). In case GROUP BY ... ORDER BY 
null is used, GROUP BY is simply removed.


mysql-test/include/mix1.inc:
  Bug#30596: Test case for InnoDB
  Here, as opposed to for MyISAM, row lookup is done using index 
  whenever the index covers the group list.
mysql-test/r/distinct.result:
  Bug#30596: Changed test case. 
  Prior to Bug#16458, These queries use temp table and filesort. The
  bug was that they used a temp table. However, that patch removed
  filesort also, in which case we can no longer gurantee correct ordering.
mysql-test/r/group_by.result:
  Bug#30596: Correct result
  The test case for IGNORE INDEX FOR GROUP BY gets degraded performance 
  (unneccesary filesort). This is due to Bug#30665, which will be fixed separately.
mysql-test/r/innodb_mysql.result:
  Bug#30596: Test result
mysql-test/t/group_by.test:
  Bug#30596: Test case
sql/sql_select.cc:
  Bug#30596: The fix: 
  - replace GROUP BY with ORDER BY unless ORDER BY [NULL|<constant>]
  - make sure to use the keys for GROUP BY in this ORDER BY.
This commit is contained in:
unknown 2007-08-28 18:01:29 +02:00
commit 22440b5387
6 changed files with 229 additions and 4 deletions
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93
mysql-test/r/group_by.result
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@ -1093,7 +1093,7 @@ id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 144
EXPLAIN SELECT a FROM t1 IGNORE INDEX FOR GROUP BY (PRIMARY,i2) GROUP BY a;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 index NULL PRIMARY 4 NULL 144 Using index
1 SIMPLE t1 index NULL PRIMARY 4 NULL 144 Using index; Using filesort
EXPLAIN SELECT a FROM t1 IGNORE INDEX FOR ORDER BY (PRIMARY,i2) ORDER BY a;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 index NULL PRIMARY 4 NULL 144 Using index; Using filesort
@ -1176,3 +1176,94 @@ old OFF
SET @@old = off;
ERROR HY000: Variable 'old' is a read only variable
DROP TABLE t1, t2;
CREATE TABLE t1(
a INT,
b INT NOT NULL,
c INT NOT NULL,
d INT,
UNIQUE KEY (c,b)
);
INSERT INTO t1 VALUES (1,1,1,50), (1,2,3,40), (2,1,3,4);
CREATE TABLE t2(
a INT,
b INT,
UNIQUE KEY(a,b)
);
INSERT INTO t2 VALUES (NULL, NULL), (NULL, NULL), (NULL, 1), (1, NULL), (1, 1), (1,2);
EXPLAIN SELECT c,b,d FROM t1 GROUP BY c,b,d;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 3 Using filesort
SELECT c,b,d FROM t1 GROUP BY c,b,d;
c b d
1 1 50
3 1 4
3 2 40
EXPLAIN SELECT c,b,d FROM t1 GROUP BY c,b,d ORDER BY NULL;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 3
SELECT c,b,d FROM t1 GROUP BY c,b,d ORDER BY NULL;
c b d
1 1 50
3 2 40
3 1 4
EXPLAIN SELECT c,b,d FROM t1 ORDER BY c,b,d;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 3 Using filesort
SELECT c,b,d FROM t1 ORDER BY c,b,d;
c b d
1 1 50
3 1 4
3 2 40
EXPLAIN SELECT c,b,d FROM t1 GROUP BY c,b;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 3 Using filesort
SELECT c,b,d FROM t1 GROUP BY c,b;
c b d
1 1 50
3 1 4
3 2 40
EXPLAIN SELECT c,b FROM t1 GROUP BY c,b;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 index NULL c 8 NULL 3 Using index
SELECT c,b FROM t1 GROUP BY c,b;
c b
1 1
3 1
3 2
EXPLAIN SELECT a,b from t2 ORDER BY a,b;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t2 index NULL a 10 NULL 6 Using index
SELECT a,b from t2 ORDER BY a,b;
a b
NULL NULL
NULL NULL
NULL 1
1 NULL
1 1
1 2
EXPLAIN SELECT a,b from t2 GROUP BY a,b;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t2 index NULL a 10 NULL 6 Using index
SELECT a,b from t2 GROUP BY a,b;
a b
NULL NULL
NULL 1
1 NULL
1 1
1 2
EXPLAIN SELECT a from t2 GROUP BY a;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t2 index NULL a 10 NULL 6 Using index
SELECT a from t2 GROUP BY a;
a
NULL
1
EXPLAIN SELECT b from t2 GROUP BY b;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t2 index NULL a 10 NULL 6 Using index; Using temporary; Using filesort
SELECT b from t2 GROUP BY b;
b
NULL
1
2
DROP TABLE t1;