diff --git a/heap/hp_write.c b/heap/hp_write.c
index 86e79c9d7ec..19215fcf017 100644
--- a/heap/hp_write.c
+++ b/heap/hp_write.c
@@ -105,7 +105,6 @@ int hp_rb_write_key(HP_INFO *info, HP_KEYDEF *keyinfo, const byte *record,
   heap_rb_param custom_arg;
   uint old_allocated;
 
-  info->last_pos= NULL; /* For heap_rnext/heap_rprev */
   custom_arg.keyseg= keyinfo->seg;
   custom_arg.key_length= hp_rb_make_key(keyinfo, info->recbuf, record, recpos);
   if (keyinfo->flag & HA_NOSAME)
diff --git a/myisam/mi_range.c b/myisam/mi_range.c
index 6655f5a7de6..2f6d9600fac 100644
--- a/myisam/mi_range.c
+++ b/myisam/mi_range.c
@@ -144,8 +144,42 @@ static ha_rows _mi_record_pos(MI_INFO *info, const byte *key, uint key_len,
   if (!(nextflag & (SEARCH_FIND | SEARCH_NO_FIND | SEARCH_LAST)))
     key_len=USE_WHOLE_KEY;
 
+  /*
+    my_handler.c:mi_compare_text() has a flag 'skip_end_space'.
+    This is set in my_handler.c:ha_key_cmp() in dependence on the
+    compare flags 'nextflag' and the column type.
+
+    TEXT columns are of type HA_KEYTYPE_VARTEXT. In this case the
+    condition is skip_end_space= ((nextflag & (SEARCH_FIND |
+    SEARCH_UPDATE)) == SEARCH_FIND).
+
+    SEARCH_FIND is used for an exact key search. The combination
+    SEARCH_FIND | SEARCH_UPDATE is used in write/update/delete
+    operations with a comment like "Not real duplicates", whatever this
+    means. From the condition above we can see that 'skip_end_space' is
+    always false for these operations. The result is that trailing space
+    counts in key comparison and hence, emtpy strings ('', string length
+    zero, but not NULL) compare less that strings starting with control
+    characters and these in turn compare less than strings starting with
+    blanks.
+
+    When estimating the number of records in a key range, we request an
+    exact search for the minimum key. This translates into a plain
+    SEARCH_FIND flag. Using this alone would lead to a 'skip_end_space'
+    compare. Empty strings would be expected above control characters.
+    Their keys would not be found because they are located below control
+    characters.
+
+    This is the reason that we add the SEARCH_UPDATE flag here. It makes
+    the key estimation compare in the same way like key write operations
+    do. Olny so we will find the keys where they have been inserted.
+
+    Adding the flag unconditionally does not hurt as it is used in the
+    above mentioned condition only. So it can safely be used together
+    with other flags.
+  */
   pos=_mi_search_pos(info,keyinfo,key_buff,key_len,
-		     nextflag | SEARCH_SAVE_BUFF,
+		     nextflag | SEARCH_SAVE_BUFF | SEARCH_UPDATE,
 		     info->s->state.key_root[inx]);
   if (pos >= 0.0)
   {
diff --git a/myisam/mi_search.c b/myisam/mi_search.c
index 75e0e500109..7016a3a6876 100644
--- a/myisam/mi_search.c
+++ b/myisam/mi_search.c
@@ -924,11 +924,16 @@ uint _mi_get_binary_pack_key(register MI_KEYDEF *keyinfo, uint nod_flag,
   /*
     Keys are compressed the following way:
 
-    prefix length    Packed length of prefix for the prev key. (1 or 3 bytes)
+    prefix length    Packed length of prefix common with prev key (1 or 3 bytes)
     for each key segment:
       [is null]        Null indicator if can be null (1 byte, zero means null)
       [length]         Packed length if varlength (1 or 3 bytes)
+      key segment      'length' bytes of key segment value
     pointer          Reference to the data file (last_keyseg->length).
+
+    get_key_length() is a macro. It gets the prefix length from 'page'
+    and puts it into 'length'. It increments 'page' by 1 or 3, depending
+    on the packed length of the prefix length.
   */
   get_key_length(length,page);
   if (length)
@@ -942,34 +947,44 @@ uint _mi_get_binary_pack_key(register MI_KEYDEF *keyinfo, uint nod_flag,
       my_errno=HA_ERR_CRASHED;
       DBUG_RETURN(0);                                 /* Wrong key */
     }
-    from=key;  from_end=key+length;
+    /* Key is packed against prev key, take prefix from prev key. */
+    from= key;
+    from_end= key + length;
   }
   else
   {
-    from=page; from_end=page_end;               /* Not packed key */
+    /* Key is not packed against prev key, take all from page buffer. */
+    from= page;
+    from_end= page_end;
   }
 
   /*
-    The trouble is that key is split in two parts:
-     The first part is in from ...from_end-1.
-     The second part starts at page
+    The trouble is that key can be split in two parts:
+      The first part (prefix) is in from .. from_end - 1.
+      The second part starts at page.
+    The split can be at every byte position. So we need to check for
+    the end of the first part before using every byte.
   */
   for (keyseg=keyinfo->seg ; keyseg->type ;keyseg++)
   {
     if (keyseg->flag & HA_NULL_PART)
     {
+      /* If prefix is used up, switch to rest. */
       if (from == from_end) { from=page;  from_end=page_end; }
       if (!(*key++ = *from++))
         continue;                               /* Null part */
     }
     if (keyseg->flag & (HA_VAR_LENGTH_PART | HA_BLOB_PART | HA_SPACE_PACK))
     {
-      /* Get length of dynamic length key part */
+      /* If prefix is used up, switch to rest. */
       if (from == from_end) { from=page;  from_end=page_end; }
+      /* Get length of dynamic length key part */
       if ((length= (*key++ = *from++)) == 255)
       {
+        /* If prefix is used up, switch to rest. */
         if (from == from_end) { from=page;  from_end=page_end; }
         length= (uint) ((*key++ = *from++)) << 8;
+        /* If prefix is used up, switch to rest. */
         if (from == from_end) { from=page;  from_end=page_end; }
         length+= (uint) ((*key++ = *from++));
       }
@@ -989,14 +1004,26 @@ uint _mi_get_binary_pack_key(register MI_KEYDEF *keyinfo, uint nod_flag,
     key+=length;
     from+=length;
   }
+  /*
+    Last segment (type == 0) contains length of data pointer.
+    If we have mixed key blocks with data pointer and key block pointer,
+    we have to copy both.
+  */
   length=keyseg->length+nod_flag;
   if ((tmp=(uint) (from_end-from)) <= length)
   {
+    /* Remaining length is less or equal max possible length. */
     memcpy(key+tmp,page,length-tmp);            /* Get last part of key */
     *page_pos= page+length-tmp;
   }
   else
   {
+    /*
+      Remaining length is greater than max possible length.
+      This can happen only if we switched to the new key bytes already.
+      'page_end' is calculated with MI_MAX_KEY_BUFF. So it can be far
+      behind the real end of the key.
+    */
     if (from_end != page_end)
     {
       DBUG_PRINT("error",("Error when unpacking key"));
@@ -1004,6 +1031,7 @@ uint _mi_get_binary_pack_key(register MI_KEYDEF *keyinfo, uint nod_flag,
       my_errno=HA_ERR_CRASHED;
       DBUG_RETURN(0);                                 /* Error */
     }
+    /* Copy data pointer and, if appropriate, key block pointer. */
     memcpy((byte*) key,(byte*) from,(size_t) length);
     *page_pos= from+length;
   }
diff --git a/mysql-test/r/heap_btree.result b/mysql-test/r/heap_btree.result
index 5b9c7f2244f..91f51a95936 100644
--- a/mysql-test/r/heap_btree.result
+++ b/mysql-test/r/heap_btree.result
@@ -280,6 +280,33 @@ a
 1
 1
 drop table t1;
+CREATE TABLE t1 (
+c1 CHAR(3),
+c2 INTEGER,
+KEY USING BTREE(c1),
+KEY USING BTREE(c2)
+) ENGINE= MEMORY;
+INSERT INTO t1 VALUES ('ABC',0), ('A',0), ('B',0), ('C',0);
+UPDATE t1 SET c2= c2 + 1 WHERE c1 = 'A';
+SELECT * FROM t1;
+c1	c2
+ABC	0
+A	1
+B	0
+C	0
+DROP TABLE t1;
+CREATE TABLE t1 (
+c1 ENUM('1', '2'),
+UNIQUE USING BTREE(c1)
+) ENGINE= MEMORY DEFAULT CHARSET= utf8;
+INSERT INTO t1 VALUES('1'), ('2');
+DROP TABLE t1;
+CREATE TABLE t1 (
+c1 SET('1', '2'),
+UNIQUE USING BTREE(c1)
+) ENGINE= MEMORY DEFAULT CHARSET= utf8;
+INSERT INTO t1 VALUES('1'), ('2');
+DROP TABLE t1;
 End of 4.1 tests
 CREATE TABLE t1(val INT, KEY USING BTREE(val)) ENGINE=memory;
 INSERT INTO t1 VALUES(0);
diff --git a/mysql-test/r/myisam.result b/mysql-test/r/myisam.result
index 83359048a8c..94f2f1f72b3 100644
--- a/mysql-test/r/myisam.result
+++ b/mysql-test/r/myisam.result
@@ -943,6 +943,156 @@ SHOW TABLE STATUS LIKE 't1';
 Name	Engine	Version	Row_format	Rows	Avg_row_length	Data_length	Max_data_length	Index_length	Data_free	Auto_increment	Create_time	Update_time	Check_time	Collation	Checksum	Create_options	Comment
 t1	MyISAM	10	Dynamic	X	X	X	72057594037927935	X	X	X	X	X	X	latin1_swedish_ci	X	max_rows=4100100100 avg_row_length=70100	
 DROP TABLE t1;
+CREATE TABLE t1 (c1 TEXT NOT NULL, KEY c1 (c1(10))) ENGINE=MyISAM;
+INSERT INTO t1 VALUES
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+(''), (''), (''), (''),
+(' B'), (' B'), (' B'), (' B');
+SELECT DISTINCT COUNT(*) FROM t1 WHERE c1 = '';
+COUNT(*)
+4
+SELECT DISTINCT length(c1), c1 FROM t1 WHERE c1 = '';
+length(c1)	c1
+0	
+SELECT DISTINCT COUNT(*) FROM t1 IGNORE INDEX (c1) WHERE c1 = '';
+COUNT(*)
+4
+SELECT DISTINCT length(c1), c1 FROM t1 IGNORE INDEX (c1) WHERE c1 = '';
+length(c1)	c1
+0	
+SELECT DISTINCT length(c1), c1 FROM t1 ORDER BY c1;
+length(c1)	c1
+0	
+2		A
+2	 B
+DROP TABLE t1;
 End of 4.1 tests
 set storage_engine=MyISAM;
 drop table if exists t1,t2,t3;
diff --git a/mysql-test/t/heap_btree.test b/mysql-test/t/heap_btree.test
index 03ba8661a3c..d5a4fb7a734 100644
--- a/mysql-test/t/heap_btree.test
+++ b/mysql-test/t/heap_btree.test
@@ -182,6 +182,37 @@ delete from t1 where a >= 2;
 select a from t1 order by a;
 drop table t1;
 
+#
+# Bug#26996 - Update of a Field in a Memory Table ends with wrong result
+#
+CREATE TABLE t1 (
+  c1 CHAR(3),
+  c2 INTEGER,
+  KEY USING BTREE(c1),
+  KEY USING BTREE(c2)
+) ENGINE= MEMORY;
+INSERT INTO t1 VALUES ('ABC',0), ('A',0), ('B',0), ('C',0);
+UPDATE t1 SET c2= c2 + 1 WHERE c1 = 'A';
+SELECT * FROM t1;
+DROP TABLE t1;
+
+#
+# Bug#24985 - UTF8 ENUM primary key on MEMORY using BTREE
+#             causes incorrect duplicate entries
+#
+CREATE TABLE t1 (
+  c1 ENUM('1', '2'),
+  UNIQUE USING BTREE(c1)
+) ENGINE= MEMORY DEFAULT CHARSET= utf8;
+INSERT INTO t1 VALUES('1'), ('2');
+DROP TABLE t1;
+CREATE TABLE t1 (
+  c1 SET('1', '2'),
+  UNIQUE USING BTREE(c1)
+) ENGINE= MEMORY DEFAULT CHARSET= utf8;
+INSERT INTO t1 VALUES('1'), ('2');
+DROP TABLE t1;
+
 --echo End of 4.1 tests
 
 #
@@ -205,3 +236,4 @@ INSERT INTO t1 VALUES(NULL),(NULL);
 DROP TABLE t1;
 
 --echo End of 5.0 tests
+
diff --git a/mysql-test/t/myisam.test b/mysql-test/t/myisam.test
index 59e3206d1c3..82d10059c65 100644
--- a/mysql-test/t/myisam.test
+++ b/mysql-test/t/myisam.test
@@ -874,6 +874,150 @@ CREATE TABLE t1 (c1 TEXT) AVG_ROW_LENGTH=70100 MAX_ROWS=4100100100;
 SHOW TABLE STATUS LIKE 't1';
 DROP TABLE t1;
 
+#
+# Bug#26231 - select count(*) on myisam table returns wrong value
+#             when index is used
+#
+CREATE TABLE t1 (c1 TEXT NOT NULL, KEY c1 (c1(10))) ENGINE=MyISAM;
+# Fill at least two key blocks. "Tab, A" must be in both blocks. 
+INSERT INTO t1 VALUES
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)), (CHAR(9,65)),
+  (''), (''), (''), (''),
+  (' B'), (' B'), (' B'), (' B');
+SELECT DISTINCT COUNT(*) FROM t1 WHERE c1 = '';
+SELECT DISTINCT length(c1), c1 FROM t1 WHERE c1 = '';
+SELECT DISTINCT COUNT(*) FROM t1 IGNORE INDEX (c1) WHERE c1 = '';
+SELECT DISTINCT length(c1), c1 FROM t1 IGNORE INDEX (c1) WHERE c1 = '';
+SELECT DISTINCT length(c1), c1 FROM t1 ORDER BY c1;
+DROP TABLE t1;
+
 --echo End of 4.1 tests
 
 
diff --git a/mysys/my_redel.c b/mysys/my_redel.c
index 1e3cfceb495..0aec395cf65 100644
--- a/mysys/my_redel.c
+++ b/mysys/my_redel.c
@@ -60,7 +60,7 @@ int my_redel(const char *org_name, const char *tmp_name, myf MyFlags)
 		  MyFlags))
       goto end;
   }
-  else if (my_delete(org_name,MyFlags))
+  else if (my_delete_allow_opened(org_name, MyFlags))
       goto end;
   if (my_rename(tmp_name,org_name,MyFlags))
     goto end;
diff --git a/sql/ha_heap.cc b/sql/ha_heap.cc
index d1a931b07f2..8838aa99c1a 100644
--- a/sql/ha_heap.cc
+++ b/sql/ha_heap.cc
@@ -604,7 +604,10 @@ int ha_heap::create(const char *name, TABLE *table_arg,
       seg->length=  (uint) key_part->length;
       seg->flag=    key_part->key_part_flag;
 
-      seg->charset= field->charset();
+      if (field->flags & (ENUM_FLAG | SET_FLAG))
+        seg->charset= &my_charset_bin;
+      else
+        seg->charset= field->charset();
       if (field->null_ptr)
       {
 	seg->null_bit= field->null_bit;
diff --git a/sql/ha_myisam.cc b/sql/ha_myisam.cc
index 10d3dbb2ec5..6d8a770175d 100644
--- a/sql/ha_myisam.cc
+++ b/sql/ha_myisam.cc
@@ -976,6 +976,22 @@ int ha_myisam::repair(THD *thd, MI_CHECK &param, bool do_optimize)
   ha_rows rows= file->state->records;
   DBUG_ENTER("ha_myisam::repair");
 
+  /*
+    Normally this method is entered with a properly opened table. If the
+    repair fails, it can be repeated with more elaborate options. Under
+    special circumstances it can happen that a repair fails so that it
+    closed the data file and cannot re-open it. In this case file->dfile
+    is set to -1. We must not try another repair without an open data
+    file. (Bug #25289)
+  */
+  if (file->dfile == -1)
+  {
+    sql_print_information("Retrying repair of: '%s' failed. "
+                          "Please try REPAIR EXTENDED or myisamchk",
+                          table->s->path);
+    DBUG_RETURN(HA_ADMIN_FAILED);
+  }
+
   param.db_name=    table->s->db;
   param.table_name= table->alias;
   param.tmpfile_createflag = O_RDWR | O_TRUNC;