Bug#47762: Incorrect result from MIN() when WHERE tests NOT

NULL column for NULL

The optimization to read MIN() and MAX() values from an
index did not properly handle comparisons with NULL
values. Fixed by giving up the particular optimization step
if there are non-NULL safe comparisons with NULL values, as 
the result is NULL anyway.

Also, Oracle copyright notice was added to all files.

mysql-test/include/min_null_cond.inc

+--replace_column 1 x 2 x 3 x 4 x 5 x 6 x 7 x 8 x 9 x
+EXPLAIN
+SELECT MIN( a ) FROM t1 WHERE a = NULL;
+SELECT MIN( a ) FROM t1 WHERE a = NULL;
+
+--replace_column 1 x 2 x 3 x 4 x 5 x 6 x 7 x 8 x 9 x
+EXPLAIN
+SELECT MIN( a ) FROM t1 WHERE a <> NULL;
+SELECT MIN( a ) FROM t1 WHERE a <> NULL;
+
+--replace_column 1 x 2 x 3 x 4 x 5 x 6 x 7 x 8 x 9 x
+EXPLAIN
+SELECT MIN( a ) FROM t1 WHERE a > NULL;
+SELECT MIN( a ) FROM t1 WHERE a > NULL;
+
+--replace_column 1 x 2 x 3 x 4 x 5 x 6 x 7 x 8 x 9 x
+EXPLAIN
+SELECT MIN( a ) FROM t1 WHERE a < NULL;
+SELECT MIN( a ) FROM t1 WHERE a < NULL;
+
+--replace_column 1 x 2 x 3 x 4 x 5 x 6 x 7 x 8 x 9 x
+EXPLAIN
+SELECT MIN( a ) FROM t1 WHERE a <=> NULL;
+SELECT MIN( a ) FROM t1 WHERE a <=> NULL;
+
+--replace_column 1 x 2 x 3 x 4 x 5 x 6 x 7 x 8 x 9 x
+EXPLAIN
+SELECT MIN( a ) FROM t1 WHERE a BETWEEN NULL AND 10;
+SELECT MIN( a ) FROM t1 WHERE a BETWEEN NULL AND 10;
+
+--replace_column 1 x 2 x 3 x 4 x 5 x 6 x 7 x 8 x 9 x
+EXPLAIN
+SELECT MIN( a ) FROM t1 WHERE a BETWEEN NULL AND NULL;
+SELECT MIN( a ) FROM t1 WHERE a BETWEEN NULL AND NULL;
+
+--replace_column 1 x 2 x 3 x 4 x 5 x 6 x 7 x 8 x 9 x
+EXPLAIN
+SELECT MIN( a ) FROM t1 WHERE a BETWEEN 10 AND NULL;
+SELECT MIN( a ) FROM t1 WHERE a BETWEEN 10 AND NULL;
+
+--replace_column 1 x 2 x 3 x 4 x 5 x 6 x 7 x 8 x 9 x
+EXPLAIN
+SELECT MIN( a ) FROM t1 WHERE a = (SELECT a FROM t1 WHERE a < 0);
+SELECT MIN( a ) FROM t1 WHERE a = (SELECT a FROM t1 WHERE a < 0);
+
+--replace_column 1 x 2 x 3 x 4 x 5 x 6 x 7 x 8 x 9 x
+EXPLAIN
+SELECT MIN( a ) FROM t1 WHERE a IS NULL;
+SELECT MIN( a ) FROM t1 WHERE a IS NULL;

mysql-test/r/group_min_max.result

@@ -2537,4 +2537,230 @@ a
 1
 2
 DROP TABLE t1;
+# 
+# Bug#47762: Incorrect result from MIN() when WHERE tests NOT NULL column
+#            for NULL
+#
+## Test for NULLs allowed
+CREATE TABLE t1 ( a INT, KEY (a) );
+INSERT INTO t1 VALUES (1), (2), (3);
+EXPLAIN
+SELECT MIN( a ) FROM t1 WHERE a = NULL;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+x	x	x	x	x	x	x	x	x	Impossible WHERE noticed after reading const tables
+SELECT MIN( a ) FROM t1 WHERE a = NULL;
+MIN( a )
+NULL
+EXPLAIN
+SELECT MIN( a ) FROM t1 WHERE a <> NULL;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+x	x	x	x	x	x	x	x	x	Impossible WHERE noticed after reading const tables
+SELECT MIN( a ) FROM t1 WHERE a <> NULL;
+MIN( a )
+NULL
+EXPLAIN
+SELECT MIN( a ) FROM t1 WHERE a > NULL;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+x	x	x	x	x	x	x	x	x	Impossible WHERE noticed after reading const tables
+SELECT MIN( a ) FROM t1 WHERE a > NULL;
+MIN( a )
+NULL
+EXPLAIN
+SELECT MIN( a ) FROM t1 WHERE a < NULL;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+x	x	x	x	x	x	x	x	x	Impossible WHERE noticed after reading const tables
+SELECT MIN( a ) FROM t1 WHERE a < NULL;
+MIN( a )
+NULL
+EXPLAIN
+SELECT MIN( a ) FROM t1 WHERE a <=> NULL;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+x	x	x	x	x	x	x	x	x	No matching min/max row
+SELECT MIN( a ) FROM t1 WHERE a <=> NULL;
+MIN( a )
+NULL
+EXPLAIN
+SELECT MIN( a ) FROM t1 WHERE a BETWEEN NULL AND 10;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+x	x	x	x	x	x	x	x	x	Impossible WHERE noticed after reading const tables
+SELECT MIN( a ) FROM t1 WHERE a BETWEEN NULL AND 10;
+MIN( a )
+NULL
+EXPLAIN
+SELECT MIN( a ) FROM t1 WHERE a BETWEEN NULL AND NULL;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+x	x	x	x	x	x	x	x	x	Impossible WHERE noticed after reading const tables
+SELECT MIN( a ) FROM t1 WHERE a BETWEEN NULL AND NULL;
+MIN( a )
+NULL
+EXPLAIN
+SELECT MIN( a ) FROM t1 WHERE a BETWEEN 10 AND NULL;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+x	x	x	x	x	x	x	x	x	Impossible WHERE noticed after reading const tables
+SELECT MIN( a ) FROM t1 WHERE a BETWEEN 10 AND NULL;
+MIN( a )
+NULL
+EXPLAIN
+SELECT MIN( a ) FROM t1 WHERE a = (SELECT a FROM t1 WHERE a < 0);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+x	x	x	x	x	x	x	x	x	Impossible WHERE noticed after reading const tables
+x	x	x	x	x	x	x	x	x	Using where; Using index
+SELECT MIN( a ) FROM t1 WHERE a = (SELECT a FROM t1 WHERE a < 0);
+MIN( a )
+NULL
+EXPLAIN
+SELECT MIN( a ) FROM t1 WHERE a IS NULL;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+x	x	x	x	x	x	x	x	x	No matching min/max row
+SELECT MIN( a ) FROM t1 WHERE a IS NULL;
+MIN( a )
+NULL
+INSERT INTO t1 VALUES (NULL), (NULL);
+EXPLAIN
+SELECT MIN( a ) FROM t1 WHERE a = NULL;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+x	x	x	x	x	x	x	x	x	Impossible WHERE noticed after reading const tables
+SELECT MIN( a ) FROM t1 WHERE a = NULL;
+MIN( a )
+NULL
+EXPLAIN
+SELECT MIN( a ) FROM t1 WHERE a <> NULL;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+x	x	x	x	x	x	x	x	x	Impossible WHERE noticed after reading const tables
+SELECT MIN( a ) FROM t1 WHERE a <> NULL;
+MIN( a )
+NULL
+EXPLAIN
+SELECT MIN( a ) FROM t1 WHERE a > NULL;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+x	x	x	x	x	x	x	x	x	Impossible WHERE noticed after reading const tables
+SELECT MIN( a ) FROM t1 WHERE a > NULL;
+MIN( a )
+NULL
+EXPLAIN
+SELECT MIN( a ) FROM t1 WHERE a < NULL;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+x	x	x	x	x	x	x	x	x	Impossible WHERE noticed after reading const tables
+SELECT MIN( a ) FROM t1 WHERE a < NULL;
+MIN( a )
+NULL
+EXPLAIN
+SELECT MIN( a ) FROM t1 WHERE a <=> NULL;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+x	x	x	x	x	x	x	x	x	Select tables optimized away
+SELECT MIN( a ) FROM t1 WHERE a <=> NULL;
+MIN( a )
+NULL
+EXPLAIN
+SELECT MIN( a ) FROM t1 WHERE a BETWEEN NULL AND 10;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+x	x	x	x	x	x	x	x	x	Impossible WHERE noticed after reading const tables
+SELECT MIN( a ) FROM t1 WHERE a BETWEEN NULL AND 10;
+MIN( a )
+NULL
+EXPLAIN
+SELECT MIN( a ) FROM t1 WHERE a BETWEEN NULL AND NULL;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+x	x	x	x	x	x	x	x	x	Impossible WHERE noticed after reading const tables
+SELECT MIN( a ) FROM t1 WHERE a BETWEEN NULL AND NULL;
+MIN( a )
+NULL
+EXPLAIN
+SELECT MIN( a ) FROM t1 WHERE a BETWEEN 10 AND NULL;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+x	x	x	x	x	x	x	x	x	Impossible WHERE noticed after reading const tables
+SELECT MIN( a ) FROM t1 WHERE a BETWEEN 10 AND NULL;
+MIN( a )
+NULL
+EXPLAIN
+SELECT MIN( a ) FROM t1 WHERE a = (SELECT a FROM t1 WHERE a < 0);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+x	x	x	x	x	x	x	x	x	Impossible WHERE noticed after reading const tables
+x	x	x	x	x	x	x	x	x	Using where; Using index
+SELECT MIN( a ) FROM t1 WHERE a = (SELECT a FROM t1 WHERE a < 0);
+MIN( a )
+NULL
+EXPLAIN
+SELECT MIN( a ) FROM t1 WHERE a IS NULL;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+x	x	x	x	x	x	x	x	x	Select tables optimized away
+SELECT MIN( a ) FROM t1 WHERE a IS NULL;
+MIN( a )
+NULL
+DROP TABLE t1;
+## Test for NOT NULLs
+CREATE TABLE t1 ( a INT NOT NULL PRIMARY KEY);
+INSERT INTO t1 VALUES (1), (2), (3);
+EXPLAIN
+SELECT MIN( a ) FROM t1 WHERE a = NULL;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+x	x	x	x	x	x	x	x	x	Impossible WHERE noticed after reading const tables
+SELECT MIN( a ) FROM t1 WHERE a = NULL;
+MIN( a )
+NULL
+EXPLAIN
+SELECT MIN( a ) FROM t1 WHERE a <> NULL;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+x	x	x	x	x	x	x	x	x	Impossible WHERE noticed after reading const tables
+SELECT MIN( a ) FROM t1 WHERE a <> NULL;
+MIN( a )
+NULL
+EXPLAIN
+SELECT MIN( a ) FROM t1 WHERE a > NULL;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+x	x	x	x	x	x	x	x	x	Impossible WHERE noticed after reading const tables
+SELECT MIN( a ) FROM t1 WHERE a > NULL;
+MIN( a )
+NULL
+EXPLAIN
+SELECT MIN( a ) FROM t1 WHERE a < NULL;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+x	x	x	x	x	x	x	x	x	Impossible WHERE noticed after reading const tables
+SELECT MIN( a ) FROM t1 WHERE a < NULL;
+MIN( a )
+NULL
+EXPLAIN
+SELECT MIN( a ) FROM t1 WHERE a <=> NULL;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+x	x	x	x	x	x	x	x	x	No matching min/max row
+SELECT MIN( a ) FROM t1 WHERE a <=> NULL;
+MIN( a )
+NULL
+EXPLAIN
+SELECT MIN( a ) FROM t1 WHERE a BETWEEN NULL AND 10;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+x	x	x	x	x	x	x	x	x	Impossible WHERE noticed after reading const tables
+SELECT MIN( a ) FROM t1 WHERE a BETWEEN NULL AND 10;
+MIN( a )
+NULL
+EXPLAIN
+SELECT MIN( a ) FROM t1 WHERE a BETWEEN NULL AND NULL;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+x	x	x	x	x	x	x	x	x	Impossible WHERE noticed after reading const tables
+SELECT MIN( a ) FROM t1 WHERE a BETWEEN NULL AND NULL;
+MIN( a )
+NULL
+EXPLAIN
+SELECT MIN( a ) FROM t1 WHERE a BETWEEN 10 AND NULL;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+x	x	x	x	x	x	x	x	x	Impossible WHERE noticed after reading const tables
+SELECT MIN( a ) FROM t1 WHERE a BETWEEN 10 AND NULL;
+MIN( a )
+NULL
+EXPLAIN
+SELECT MIN( a ) FROM t1 WHERE a = (SELECT a FROM t1 WHERE a < 0);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+x	x	x	x	x	x	x	x	x	Impossible WHERE noticed after reading const tables
+x	x	x	x	x	x	x	x	x	Using where; Using index
+SELECT MIN( a ) FROM t1 WHERE a = (SELECT a FROM t1 WHERE a < 0);
+MIN( a )
+NULL
+EXPLAIN
+SELECT MIN( a ) FROM t1 WHERE a IS NULL;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+x	x	x	x	x	x	x	x	x	Impossible WHERE
+SELECT MIN( a ) FROM t1 WHERE a IS NULL;
+MIN( a )
+NULL
+DROP TABLE t1;
 End of 5.1 tests

mysql-test/t/group_min_max.test

@@ -1054,4 +1054,23 @@ SELECT 1 AS c, b FROM t1 WHERE b IN (1,2) GROUP BY c, b;
 SELECT a FROM t1 WHERE b=1;
 DROP TABLE t1;
 
+--echo # 
+--echo # Bug#47762: Incorrect result from MIN() when WHERE tests NOT NULL column
+--echo #            for NULL
+--echo #
+
+--echo ## Test for NULLs allowed
+CREATE TABLE t1 ( a INT, KEY (a) );
+INSERT INTO t1 VALUES (1), (2), (3);
+--source include/min_null_cond.inc
+INSERT INTO t1 VALUES (NULL), (NULL);
+--source include/min_null_cond.inc
+DROP TABLE t1;
+
+--echo ## Test for NOT NULLs
+CREATE TABLE t1 ( a INT NOT NULL PRIMARY KEY);
+INSERT INTO t1 VALUES (1), (2), (3);
+--source include/min_null_cond.inc
+DROP TABLE t1;
+
 --echo End of 5.1 tests

sql/field.h

-/* Copyright 2000-2008 MySQL AB, 2008, 2009 Sun Microsystems, Inc.
+/* Copyright (c) 2000, 2010 Oracle and/or its affiliates. All rights reserved.
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -11,7 +11,7 @@
 
    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
-   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA */
+   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA */
 
 /*
   Because of the function new_field() all field classes that have static
@@ -55,7 +55,11 @@ public:
   static void operator delete(void *ptr_arg, size_t size) { TRASH(ptr_arg, size); }
 
   uchar		*ptr;			// Position to field in record
-  uchar		*null_ptr;		// Byte where null_bit is
+  /**
+     Byte where the @c NULL bit is stored inside a record. If this Field is a
+     @c NOT @c NULL field, this member is @c NULL.
+  */
+  uchar		*null_ptr;
   /*
     Note that you can use table->in_use as replacement for current_thd member 
     only inside of val_*() and store() members (e.g. you can't use it in cons)
@@ -261,6 +265,9 @@ public:
   inline void set_notnull(my_ptrdiff_t row_offset= 0)
     { if (null_ptr) null_ptr[row_offset]&= (uchar) ~null_bit; }
   inline bool maybe_null(void) { return null_ptr != 0 || table->maybe_null; }
+  /**
+     Signals that this field is NULL-able.
+  */
   inline bool real_maybe_null(void) { return null_ptr != 0; }
 
   enum {

sql/opt_sum.cc

-/* Copyright (C) 2000-2003 MySQL AB
+/* Copyright (c) 2000, 2010 Oracle and/or its affiliates. All rights reserved.
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -11,7 +11,7 @@
 
    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
-   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA */
+   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA */
 
 
 /**
@@ -96,7 +96,7 @@ static ulonglong get_exact_record_count(TABLE_LIST *tables)
   @param conds                 WHERE clause
 
   @note
-    This function is only called for queries with sum functions and no
+    This function is only called for queries with aggregate functions and no
     GROUP BY part. This means that the result set shall contain a single
     row only
 
@@ -559,31 +559,57 @@ bool simple_pred(Item_func *func_item, Item **args, bool *inv_order)
 /**
   Check whether a condition matches a key to get {MAX|MIN}(field):.
 
-     For the index specified by the keyinfo parameter, index that
-     contains field as its component (field_part), the function
-     checks whether the condition cond is a conjunction and all its
-     conjuncts referring to the columns of the same table as column
-     field are one of the following forms:
-     - f_i= const_i or const_i= f_i or f_i is null,
-     where f_i is part of the index
-     - field {<|<=|>=|>|=} const or const {<|<=|>=|>|=} field
-     - field between const1 and const2
-
-  @param[in]     max_fl         Set to 1 if we are optimising MAX()
-  @param[in,out] ref            Reference to the structure we store the key
-    value
-  @param[in]     keyinfo        Reference to the key info
-  @param[in]     field_part     Pointer to the key part for the field
-  @param[in]     cond           WHERE condition
-  @param[in,out] key_part_used  Map of matchings parts
-  @param[in,out] range_fl       Says whether including key will be used
-  @param[out]    prefix_len     Length of common key part for the range
-    where MAX/MIN is searched for
+   For the index specified by the keyinfo parameter and an index that
+   contains the field as its component (field_part), the function
+   checks whether 
+
+   - the condition cond is a conjunction, 
+   - all of its conjuncts refer to columns of the same table, and
+   - each conjunct is on one of the following forms:
+     - f_i = const_i or const_i = f_i or f_i IS NULL,
+       where f_i is part of the index
+     - field {<|<=|>=|>|=} const
+     - const {<|<=|>=|>|=} field
+     - field BETWEEN const_1 AND const_2
+
+   As a side-effect, the key value to be used for looking up the MIN/MAX value
+   is actually stored inside the Field object. An interesting feature is that
+   the function will find the most restrictive endpoint by over-eager
+   evaluation of the @c WHERE condition. It continually stores the current
+   endpoint inside the Field object. For a query such as
+
+   @code
+   SELECT MIN(a) FROM t1 WHERE a > 3 AND a > 5;
+   @endcode
+
+   the algorithm will recurse over the conjuction, storing first a 3 in the
+   field. In the next recursive invocation the expression a > 5 is evaluated
+   as 3 > 5 (Due to the dual nature of Field objects as value carriers and
+   field identifiers), which will obviously fail, leading to 5 being stored in
+   the Field object.
+   
+   @param[in]     max_fl         Set to true if we are optimizing MAX(),
+                                 false means we are optimizing %MIN()
+   @param[in, out] ref           Reference to the structure where the function 
+                                 stores the key value
+   @param[in]     keyinfo        Reference to the key info
+   @param[in]     field_part     Pointer to the key part for the field
+   @param[in]     cond           WHERE condition
+   @param[in,out] key_part_used  Map of matchings parts. The function will output
+                                 the set of key parts actually being matched in 
+                                 this set, yet it relies on the caller to 
+                                 initialize the value to zero. This is due 
+                                 to the fact that this value is passed 
+                                 recursively.
+   @param[in,out] range_fl       Says whether endpoints use strict greater/less 
+                                 than.
+   @param[out]    prefix_len     Length of common key part for the range
+                                 where MAX/MIN is searched for
 
   @retval
-    0        Index can't be used.
+    false    Index can't be used.
   @retval
-    1        We can use index to get MIN/MAX value
+    true     We can use the index to get MIN/MAX value
 */
 
 static bool matching_cond(bool max_fl, TABLE_REF *ref, KEY *keyinfo, 
@@ -620,17 +646,20 @@ static bool matching_cond(bool max_fl, TABLE_REF *ref, KEY *keyinfo,
     return 0;                                 // Not operator, can't optimize
 
   bool eq_type= 0;                            // =, <=> or IS NULL
+  bool is_null_safe_eq= FALSE;                // The operator is NULL safe, e.g. <=> 
   bool noeq_type= 0;                          // < or >  
   bool less_fl= 0;                            // < or <= 
-  bool is_null= 0;
-  bool between= 0;
+  bool is_null= 0;                            // IS NULL
+  bool between= 0;                            // BETWEEN ... AND ... 
 
   switch (((Item_func*) cond)->functype()) {
   case Item_func::ISNULL_FUNC:
     is_null= 1;     /* fall through */
   case Item_func::EQ_FUNC:
+    eq_type= TRUE;
+    break;
   case Item_func::EQUAL_FUNC:
-    eq_type= 1;
+    eq_type= is_null_safe_eq= TRUE;
     break;
   case Item_func::LT_FUNC:
     noeq_type= 1;   /* fall through */
@@ -658,6 +687,10 @@ static bool matching_cond(bool max_fl, TABLE_REF *ref, KEY *keyinfo,
   if (!simple_pred((Item_func*) cond, args, &inv))
     return 0;
 
+  if (!is_null_safe_eq && !is_null &&
+      (args[1]->is_null() || (between && args[2]->is_null())))
+    return FALSE;
+
   if (inv && !eq_type)
     less_fl= 1-less_fl;                         // Convert '<' -> '>' (etc)
 
@@ -708,15 +741,16 @@ static bool matching_cond(bool max_fl, TABLE_REF *ref, KEY *keyinfo,
       - field {>|>=} const, when searching for MIN
     */
 
-    if (is_null)
+    if (is_null || (is_null_safe_eq && args[1]->is_null()))
     {
       part->field->set_null();
       *key_ptr= (uchar) 1;
     }
     else
     {
-      store_val_in_field(part->field, args[between && max_fl ? 2 : 1],
-                         CHECK_FIELD_IGNORE);
+      /* Update endpoints for MAX/MIN, see function comment. */
+      Item *value= args[between && max_fl ? 2 : 1];
+      store_val_in_field(part->field, value, CHECK_FIELD_IGNORE);
       if (part->null_bit) 
         *key_ptr++= (uchar) test(part->field->is_null());
       part->field->get_key_image(key_ptr, part->length, Field::itRAW);