bk commit into 5.0 tree (mhansson:1.2432) BUG#27573

[mhansson]

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ChangeSet@stripped, 2007-04-23 18:00:43+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 18:00:41+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 18:00:41+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 18:00:41+03:00, mhansson@stripped +65 -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 18:00:41 +03:00
@@ -206,12 +206,58 @@ 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 
+          {
+            /*
+              Read the smallest value with the key constructed by
+              find_key_for_maxmin. If the interval is open, we skip 
+              the first tuple. If there are no more tuples, read the one 
+              we skipped, we may not need to fail after all.
+            */
+            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
+            {
+              /*
+                Open interval: 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)) 
+              {
+                /*
+                  If there's a NULL value in the last column of the
+                  tuple we skipped earlier, the original query is a
+                  MIN(c) and we should return that NULL.
+                */
+                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())
+                  /*
+                    OK, so it's not a NULL. 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 +785,23 @@ 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 18:00:41 +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 18:00:41 +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