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ChangeSet@stripped, 2007-04-23 13:53:30+03:00, mhansson@stripped +3 -0
Bug#27573: MIN() on an indexed column which is always NULL sets _other_ results
to NULL
We have the following case:
SELECT MIN(keypart2),... FROM t1 WHERE keypart1 = constant;
There is an optimization which will substitute a constant for
MIN(keypart2), inserting the 1) minimum non-null value where the
WHERE clause still matches, or 2) null if there are only NULL
values for keypart2. If no row matches, the result will be 3) a row
of NULLs.
The previous implementation skipped step 2, and went straight to
a row of NULLs.
mysql-test/r/func_group.result@stripped, 2007-04-23 13:53:24+03:00, mhansson@stripped +44 -0
Bug #27573: MIN() on an indexed column which is always NULL sets
_other_ results to NULL
Correct result
mysql-test/t/func_group.test@stripped, 2007-04-23 13:53:25+03:00, mhansson@stripped +33 -0
Bug #27573: MIN() on an indexed column which is always NULL sets
_other_ results to NULL
test case
sql/opt_sum.cc@stripped, 2007-04-23 13:53:25+03:00, mhansson@stripped +71 -9
Bug #27573: MIN() on an indexed column which is always NULL sets
_other_ results to NULL
Added code that will try to read the
first non-null value for a given complete-field prefix, second
choice is to read the null, and lastly set the error code if no row
is found.
# This is a BitKeeper patch. What follows are the unified diffs for the
# set of deltas contained in the patch. The rest of the patch, the part
# that BitKeeper cares about, is below these diffs.
# User: mhansson
# Host: linux-st28.site
# Root: /home/martin/mysql/src/5.0o-bug27573
--- 1.61/sql/opt_sum.cc 2007-01-30 23:09:25 +02:00
+++ 1.62/sql/opt_sum.cc 2007-04-23 13:53:25 +03:00
@@ -206,12 +206,64 @@ int opt_sum_query(TABLE_LIST *tables, Li
if (!ref.key_length)
error= table->file->index_first(table->record[0]);
- else
- error= table->file->index_read(table->record[0],key_buff,
- ref.key_length,
- range_fl & NEAR_MIN ?
- HA_READ_AFTER_KEY :
- HA_READ_KEY_OR_NEXT);
+ else
+ {
+ /*
+ This piece of code reads the minimum value for a key
+ prefix. If the interval is open, The next different
+ tuple will be read, if it exists. If it doesn't, the
+ function will read the tuple before the read one to see
+ if the n:th keypart is NULL for this column. In that
+ case the latter record will be returned. Otherwise the
+ index position is restored and
+ error=HA_ERR_KEY_NOT_FOUND.
+ */
+ if (!(range_fl & NEAR_MIN)) // closed interval
+ /*
+ This means that either
+ - it has been determined that there are no NULLs in
+ the column we are searching, or
+ - we have a >= predicate for the wanted value.
+ */
+ error= table->file->index_read(table->record[0], ref.key_buff,
+ ref.key_length,
+ HA_READ_KEY_OR_NEXT);
+ else
+ {
+ /*
+ We are either doing a MIN(c) and NULLs are known to be
+ in this column, or we have a predicate c >
+ something. Either way, we want the next record.
+ */
+ error= table->file->index_read(table->record[0], ref.key_buff,
+ ref.key_length, HA_READ_AFTER_KEY);
+ /*
+ Are we either at the end of the index, or outside
+ of the group formed by prefix?
+ */
+ if (error == HA_ERR_KEY_NOT_FOUND ||
+ key_cmp_if_same(table, ref.key_buff, ref.key, prefix_len))
+ {
+ /*
+ Depending on what we're doing, we should take a step
+ backward, or just keep what we have and exit (even
+ if we have nothing) However, in order to know, we
+ must take that step backards.
+ */
+ error= table->file->index_read(table->record[0], ref.key_buff,
+ ref.key_length,
+ HA_READ_KEY_OR_PREV);
+ if (!item_field->field->is_null())
+ /*
+ So, after taking a step backwards, we find that the sought
+ value for the column is not NULL. This means that we were
+ *not* looking for a MIN() value, so fail.
+ */
+ error= HA_ERR_KEY_NOT_FOUND;
+ }
+
+ }
+ }
if (!error && reckey_in_range(0, &ref, item_field->field,
conds, range_fl, prefix_len))
error= HA_ERR_KEY_NOT_FOUND;
@@ -739,13 +791,23 @@ static bool find_key_for_maxmin(bool max
if (!max_fl && key_part_used == key_part_to_use && part->null_bit)
{
/*
- SELECT MIN(key_part2) FROM t1 WHERE key_part1=const
- If key_part2 may be NULL, then we want to find the first row
- that is not null
+ SELECT MIN(key_part2) FROM t1 WHERE key_part1=const
+
+ If key_part2 may be NULL, then we want to find the first
+ row that is not null. So we set the first byte that
+ comes after key_part1 to 1. This means that the key
+ buffer now contains {const, NULL}. This key buffer will
+ be passed to the handler along with a flag, NEAR_MIN,
+ that tells it to retrieve the record that is stored
+ after this key buffer. This is handled by function
+ read_next_or_current(). This function is smart enough to
+ backtrack and see if the original key {const, NULL} is
+ present if there is no key after it.
*/
ref->key_buff[ref->key_length]= 1;
ref->key_length+= part->store_length;
*range_fl&= ~NO_MIN_RANGE;
+ /* Exclusive interval, we prefer the value after this key */
*range_fl|= NEAR_MIN; // > NULL
}
/*
--- 1.59/mysql-test/r/func_group.result 2007-02-27 09:01:57 +02:00
+++ 1.60/mysql-test/r/func_group.result 2007-04-23 13:53:24 +03:00
@@ -1321,4 +1321,48 @@ SELECT a,AVG(DISTINCT b) AS average FROM
a average
1 32768.5000
DROP TABLE t1;
+CREATE TABLE t1 ( a INT, b INT, KEY(a) );
+INSERT INTO t1 VALUES (NULL, 1), (NULL, 2);
+EXPLAIN SELECT MIN(a), MIN(b) FROM t1;
+id select_type table type possible_keys key key_len ref rows Extra
+1 SIMPLE t1 ALL NULL NULL NULL NULL 2
+SELECT MIN(a), MIN(b) FROM t1;
+MIN(a) MIN(b)
+NULL 1
+CREATE TABLE t2( a INT, b INT, c INT, KEY(a, b) );
+INSERT INTO t2 ( a, b, c ) VALUES ( 1, NULL, 2 ), ( 1, 3, 4 ), ( 1, 4, 4 );
+EXPLAIN SELECT MIN(b), MIN(c) FROM t2 WHERE a = 1;
+id select_type table type possible_keys key key_len ref rows Extra
+1 SIMPLE t2 ref a a 5 const 2 Using where
+SELECT MIN(b), MIN(c) FROM t2 WHERE a = 1;
+MIN(b) MIN(c)
+3 2
+CREATE TABLE t3 (a INT, b INT, c int, KEY(a, b));
+INSERT INTO t3 VALUES (1, NULL, 1), (2, NULL, 2), (2, NULL, 2), (3, NULL, 3);
+EXPLAIN SELECT MIN(a), MIN(b) FROM t3 where a = 2;
+id select_type table type possible_keys key key_len ref rows Extra
+1 SIMPLE NULL NULL NULL NULL NULL NULL NULL Select tables optimized away
+SELECT MIN(a), MIN(b) FROM t3 where a = 2;
+MIN(a) MIN(b)
+2 NULL
+CREATE TABLE t4 (a INT, b INT, c int, KEY(a, b));
+INSERT INTO t4 VALUES (1, 1, 1), (2, NULL, 2), (2, NULL, 2), (3, 1, 3);
+EXPLAIN SELECT MIN(a), MIN(b) FROM t4 where a = 2;
+id select_type table type possible_keys key key_len ref rows Extra
+1 SIMPLE NULL NULL NULL NULL NULL NULL NULL Select tables optimized away
+SELECT MIN(a), MIN(b) FROM t4 where a = 2;
+MIN(a) MIN(b)
+2 NULL
+SELECT MIN(b), min(c) FROM t4 where a = 2;
+MIN(b) min(c)
+NULL 2
+CREATE TABLE t5( a INT, b INT, KEY( a, b) );
+INSERT INTO t5 VALUES( 1, 1 ), ( 1, 2 );
+EXPLAIN SELECT MIN(a), MIN(b) FROM t5 WHERE a = 1;
+id select_type table type possible_keys key key_len ref rows Extra
+1 SIMPLE NULL NULL NULL NULL NULL NULL NULL Select tables optimized away
+SELECT MIN(a), MIN(b) FROM t5 WHERE a = 1;
+MIN(a) MIN(b)
+1 1
+DROP TABLE t1, t2, t3, t4, t5;
End of 5.0 tests
--- 1.54/mysql-test/t/func_group.test 2007-02-27 09:01:57 +02:00
+++ 1.55/mysql-test/t/func_group.test 2007-04-23 13:53:25 +03:00
@@ -817,5 +817,38 @@ SELECT a,AVG(DISTINCT b) AS average FROM
DROP TABLE t1;
+#
+# Bug #27573: MIN() on an indexed column which is always NULL sets _other_
+# results to NULL
+#
+CREATE TABLE t1 ( a INT, b INT, KEY(a) );
+INSERT INTO t1 VALUES (NULL, 1), (NULL, 2);
+EXPLAIN SELECT MIN(a), MIN(b) FROM t1;
+SELECT MIN(a), MIN(b) FROM t1;
+
+CREATE TABLE t2( a INT, b INT, c INT, KEY(a, b) );
+INSERT INTO t2 ( a, b, c ) VALUES ( 1, NULL, 2 ), ( 1, 3, 4 ), ( 1, 4, 4 );
+EXPLAIN SELECT MIN(b), MIN(c) FROM t2 WHERE a = 1;
+SELECT MIN(b), MIN(c) FROM t2 WHERE a = 1;
+
+CREATE TABLE t3 (a INT, b INT, c int, KEY(a, b));
+INSERT INTO t3 VALUES (1, NULL, 1), (2, NULL, 2), (2, NULL, 2), (3, NULL, 3);
+EXPLAIN SELECT MIN(a), MIN(b) FROM t3 where a = 2;
+SELECT MIN(a), MIN(b) FROM t3 where a = 2;
+
+CREATE TABLE t4 (a INT, b INT, c int, KEY(a, b));
+INSERT INTO t4 VALUES (1, 1, 1), (2, NULL, 2), (2, NULL, 2), (3, 1, 3);
+EXPLAIN SELECT MIN(a), MIN(b) FROM t4 where a = 2;
+SELECT MIN(a), MIN(b) FROM t4 where a = 2;
+SELECT MIN(b), min(c) FROM t4 where a = 2;
+
+CREATE TABLE t5( a INT, b INT, KEY( a, b) );
+INSERT INTO t5 VALUES( 1, 1 ), ( 1, 2 );
+EXPLAIN SELECT MIN(a), MIN(b) FROM t5 WHERE a = 1;
+SELECT MIN(a), MIN(b) FROM t5 WHERE a = 1;
+
+
+DROP TABLE t1, t2, t3, t4, t5;
+
###
--echo End of 5.0 tests
| Thread |
|---|
| • bk commit into 5.0 tree (mhansson:1.2432) BUG#27573 | mhansson | 23 Apr |
