Addressed the following issue from the review of the patch for

engine-independent statistics.
When the primary key was dropped or changed statistics on secondary
indexes for the prefixes that included components of the primary 
key was not removed from the table mysql.index_stats.

Also fixed: in the some cases when a column was changed statistics
on the indexes that included this column was not removed from the
table mysql.index_stats.

Also disabled the test mdev-504 for --ps-protocol.

mysql-test/r/statistics.result

@@ -499,14 +499,9 @@ test	t1	f	1	5	0.2000	1.0000	6.4000
 SELECT * FROM mysql.index_stats;
 db_name	table_name	index_name	prefix_arity	avg_frequency
 test	t1	PRIMARY	1	1.0000
-test	t1	idx1	1	6.4000
-test	t1	idx1	2	1.6875
 test	t1	idx2	1	7.0000
 test	t1	idx2	2	2.3846
 test	t1	idx3	1	8.5000
-test	t1	idx4	1	6.2000
-test	t1	idx4	2	1.6875
-test	t1	idx4	3	1.1304
 ALTER TABLE t1 CHANGE COLUMN x b varchar(32);
 SHOW CREATE TABLE t1;
 Table	Create Table
@@ -590,14 +585,9 @@ test	t1	f	1	5	0.2000	1.0000	6.4000
 SELECT * FROM mysql.index_stats;
 db_name	table_name	index_name	prefix_arity	avg_frequency
 test	t1	PRIMARY	1	1.0000
-test	t1	idx4	3	1.1304
-test	t1	idx4	2	1.6875
 test	t1	idx2	1	7.0000
 test	t1	idx2	2	2.3846
 test	t1	idx3	1	8.5000
-test	t1	idx4	1	6.2000
-test	t1	idx1	2	1.6875
-test	t1	idx1	1	6.4000
 ALTER TABLE t1 CHANGE COLUMN x b varchar(32);
 SHOW CREATE TABLE t1;
 Table	Create Table
@@ -943,6 +933,7 @@ test	t1	idx4	3	1.1304
 CREATE TABLE t2 LIKE t1;
 ALTER TABLE t2 ENGINE=InnoDB;
 INSERT INTO t2 SELECT * FROM t1;
+set optimizer_switch='extended_keys=off';
 ANALYZE TABLE t2;
 Table	Op	Msg_type	Msg_text
 test.t2	analyze	status	OK
@@ -987,6 +978,142 @@ test	t2	idx4	3	1.1304
 DELETE FROM mysql.table_stats;
 DELETE FROM mysql.column_stats;
 DELETE FROM mysql.index_stats;
+set optimizer_switch='extended_keys=on';
+ANALYZE TABLE t2;
+Table	Op	Msg_type	Msg_text
+test.t2	analyze	status	OK
+SELECT * FROM mysql.table_stats;
+db_name	table_name	cardinality
+test	t2	40
+SELECT * FROM mysql.column_stats ORDER BY column_name;
+db_name	table_name	column_name	min_value	max_value	nulls_ratio	avg_length	avg_frequency
+test	t2	a	0	49	0.0000	4.0000	1.0000
+test	t2	b	vvvvvvvvvvvvv	zzzzzzzzzzzzzzzzzz	0.2000	17.1250	6.4000
+test	t2	c	aaaa	dddddddd	0.1250	6.6571	7.0000
+test	t2	d	1989-03-12	1999-07-23	0.1500	3.0000	8.5000
+test	t2	e	0.01	0.112	0.2250	8.0000	6.2000
+test	t2	f	1	5	0.2000	1.0000	6.4000
+SELECT * FROM mysql.index_stats ORDER BY index_name, prefix_arity, table_name;
+db_name	table_name	index_name	prefix_arity	avg_frequency
+test	t2	PRIMARY	1	1.0000
+test	t2	idx1	1	6.4000
+test	t2	idx1	2	1.6875
+test	t2	idx1	3	1.0000
+test	t2	idx2	1	7.0000
+test	t2	idx2	2	2.3846
+test	t2	idx2	3	1.0000
+test	t2	idx3	1	8.5000
+test	t2	idx3	2	1.0000
+test	t2	idx4	1	6.2000
+test	t2	idx4	2	1.6875
+test	t2	idx4	3	1.1304
+test	t2	idx4	4	1.0000
+ALTER TABLE t2 DROP PRIMARY KEY, DROP INDEX idx1;
+SELECT * FROM mysql.index_stats ORDER BY index_name, prefix_arity, table_name;
+db_name	table_name	index_name	prefix_arity	avg_frequency
+test	t2	idx2	1	7.0000
+test	t2	idx2	2	2.3846
+test	t2	idx3	1	8.5000
+test	t2	idx4	1	6.2000
+test	t2	idx4	2	1.6875
+test	t2	idx4	3	1.1304
+UPDATE t2 SET b=0 WHERE b IS NULL;
+ALTER TABLE t2 ADD PRIMARY KEY (a,b);
+SELECT * FROM mysql.index_stats ORDER BY index_name, prefix_arity, table_name;
+db_name	table_name	index_name	prefix_arity	avg_frequency
+test	t2	idx2	1	7.0000
+test	t2	idx2	2	2.3846
+test	t2	idx3	1	8.5000
+test	t2	idx4	1	6.2000
+test	t2	idx4	2	1.6875
+test	t2	idx4	3	1.1304
+ANALYZE TABLE t2 PERSISTENT FOR COLUMNS() INDEXES ALL;
+Table	Op	Msg_type	Msg_text
+test.t2	analyze	status	OK
+SELECT * FROM mysql.index_stats ORDER BY index_name, prefix_arity, table_name;
+db_name	table_name	index_name	prefix_arity	avg_frequency
+test	t2	PRIMARY	1	1.0000
+test	t2	PRIMARY	2	1.0000
+test	t2	idx2	1	7.0000
+test	t2	idx2	2	2.3846
+test	t2	idx2	3	1.0000
+test	t2	idx2	4	1.0000
+test	t2	idx3	1	8.5000
+test	t2	idx3	2	1.0000
+test	t2	idx3	3	1.0000
+test	t2	idx4	1	6.2000
+test	t2	idx4	2	1.7222
+test	t2	idx4	3	1.1154
+test	t2	idx4	4	1.0000
+ALTER TABLE t2 CHANGE COLUMN b b varchar(30);
+SELECT * FROM mysql.index_stats ORDER BY index_name, prefix_arity, table_name;
+db_name	table_name	index_name	prefix_arity	avg_frequency
+test	t2	idx2	1	7.0000
+test	t2	idx2	2	2.3846
+test	t2	idx3	1	8.5000
+ANALYZE TABLE t2 PERSISTENT FOR COLUMNS ALL INDEXES ALL;
+Table	Op	Msg_type	Msg_text
+test.t2	analyze	status	OK
+SELECT * FROM mysql.index_stats ORDER BY index_name, prefix_arity, table_name;
+db_name	table_name	index_name	prefix_arity	avg_frequency
+test	t2	PRIMARY	1	1.0000
+test	t2	PRIMARY	2	1.0000
+test	t2	idx2	1	7.0000
+test	t2	idx2	2	2.3846
+test	t2	idx2	3	1.0000
+test	t2	idx2	4	1.0000
+test	t2	idx3	1	8.5000
+test	t2	idx3	2	1.0000
+test	t2	idx3	3	1.0000
+test	t2	idx4	1	6.2000
+test	t2	idx4	2	1.7222
+test	t2	idx4	3	1.1154
+test	t2	idx4	4	1.0000
+ALTER TABLE t2 CHANGE COLUMN b b varchar(32);
+SELECT * FROM mysql.index_stats ORDER BY index_name, prefix_arity, table_name;
+db_name	table_name	index_name	prefix_arity	avg_frequency
+test	t2	idx2	1	7.0000
+test	t2	idx2	2	2.3846
+test	t2	idx3	1	8.5000
+ANALYZE TABLE t2 PERSISTENT FOR COLUMNS ALL INDEXES ALL;
+Table	Op	Msg_type	Msg_text
+test.t2	analyze	status	OK
+SELECT * FROM mysql.index_stats ORDER BY index_name, prefix_arity, table_name;
+db_name	table_name	index_name	prefix_arity	avg_frequency
+test	t2	PRIMARY	1	1.0000
+test	t2	PRIMARY	2	1.0000
+test	t2	idx2	1	7.0000
+test	t2	idx2	2	2.3846
+test	t2	idx2	3	1.0000
+test	t2	idx2	4	1.0000
+test	t2	idx3	1	8.5000
+test	t2	idx3	2	1.0000
+test	t2	idx3	3	1.0000
+test	t2	idx4	1	6.2000
+test	t2	idx4	2	1.7222
+test	t2	idx4	3	1.1154
+test	t2	idx4	4	1.0000
+ALTER TABLE t2 DROP COLUMN b;
+SELECT * FROM mysql.index_stats ORDER BY index_name, prefix_arity, table_name;
+db_name	table_name	index_name	prefix_arity	avg_frequency
+test	t2	idx2	1	7.0000
+test	t2	idx2	2	2.3846
+test	t2	idx3	1	8.5000
+ANALYZE TABLE t2 PERSISTENT FOR COLUMNS() INDEXES ALL;
+Table	Op	Msg_type	Msg_text
+test.t2	analyze	status	OK
+SELECT * FROM mysql.index_stats ORDER BY index_name, prefix_arity, table_name;
+db_name	table_name	index_name	prefix_arity	avg_frequency
+test	t2	PRIMARY	1	1.0000
+test	t2	idx2	1	7.0000
+test	t2	idx2	2	2.3846
+test	t2	idx2	3	1.0000
+test	t2	idx3	1	8.5000
+test	t2	idx3	2	1.0000
+test	t2	idx4	1	6.2000
+test	t2	idx4	2	2.2308
+test	t2	idx4	3	1.0000
+set optimizer_switch='extended_keys=off';
 ALTER TABLE t1
 DROP INDEX idx1,
 DROP INDEX idx4;
@@ -994,11 +1121,34 @@ ALTER TABLE t1
 MODIFY COLUMN b text,
 ADD INDEX idx1 (b(4), e), 
 ADD INDEX idx4 (e, b(4), d);
+SELECT * FROM mysql.column_stats;
+db_name	table_name	column_name	min_value	max_value	nulls_ratio	avg_length	avg_frequency
+test	t2	a	0	49	0.0000	4.0000	1.0000
+test	t2	c	aaaa	dddddddd	0.1250	6.6571	7.0000
+test	t2	d	1989-03-12	1999-07-23	0.1500	3.0000	8.5000
+test	t2	e	0.01	0.112	0.2250	8.0000	6.2000
+test	t2	f	1	5	0.2000	1.0000	6.4000
+SELECT * FROM mysql.index_stats;
+db_name	table_name	index_name	prefix_arity	avg_frequency
+test	t2	idx3	1	8.5000
+test	t2	idx3	2	1.0000
+test	t2	idx2	3	1.0000
+test	t2	idx2	1	7.0000
+test	t2	idx2	2	2.3846
+test	t2	idx4	3	1.0000
+test	t2	idx4	1	6.2000
+test	t2	idx4	2	2.2308
+test	t2	PRIMARY	1	1.0000
 ANALYZE TABLE t1;
 Table	Op	Msg_type	Msg_text
 test.t1	analyze	status	OK
 SELECT * FROM mysql.column_stats;
 db_name	table_name	column_name	min_value	max_value	nulls_ratio	avg_length	avg_frequency
+test	t2	a	0	49	0.0000	4.0000	1.0000
+test	t2	c	aaaa	dddddddd	0.1250	6.6571	7.0000
+test	t2	d	1989-03-12	1999-07-23	0.1500	3.0000	8.5000
+test	t2	e	0.01	0.112	0.2250	8.0000	6.2000
+test	t2	f	1	5	0.2000	1.0000	6.4000
 test	t1	a	0	49	0.0000	4.0000	1.0000
 test	t1	c	aaaa	dddddddd	0.1250	6.6571	7.0000
 test	t1	d	1989-03-12	1999-07-23	0.1500	3.0000	8.5000
@@ -1007,9 +1157,18 @@ test	t1	f	1	5	0.2000	1.0000	6.4000
 test	t1	b	NULL	NULL	0.2000	17.1250	NULL
 SELECT * FROM mysql.index_stats;
 db_name	table_name	index_name	prefix_arity	avg_frequency
-test	t1	PRIMARY	1	1.0000
-test	t1	idx3	1	8.5000
+test	t2	idx3	1	8.5000
+test	t2	idx3	2	1.0000
+test	t2	idx2	3	1.0000
+test	t2	idx2	1	7.0000
+test	t2	idx2	2	2.3846
 test	t1	idx2	1	7.0000
+test	t1	idx3	1	8.5000
+test	t1	PRIMARY	1	1.0000
+test	t2	idx4	3	1.0000
+test	t2	idx4	1	6.2000
+test	t2	idx4	2	2.2308
+test	t2	PRIMARY	1	1.0000
 test	t1	idx2	2	2.3846
 test	t1	idx1	1	NULL
 test	t1	idx1	2	NULL
@@ -1057,28 +1216,6 @@ test	t1	idx1	2	NULL
 test	t1	idx4	1	6.2000
 test	t1	idx4	2	NULL
 test	t1	idx4	3	NULL
-SELECT * FROM mysql.table_stats;
-db_name	table_name	cardinality
-test	t1	40
-SELECT * FROM mysql.column_stats;
-db_name	table_name	column_name	min_value	max_value	nulls_ratio	avg_length	avg_frequency
-test	t1	a	0	49	0.0000	4.0000	1.0000
-test	t1	c	aaaa	dddddddd	0.1250	6.6571	7.0000
-test	t1	d	1989-03-12	1999-07-23	0.1500	3.0000	8.5000
-test	t1	e	0.01	0.112	0.2250	8.0000	6.2000
-test	t1	f	1	5	0.2000	1.0000	6.4000
-test	t1	b	NULL	NULL	0.2000	17.1250	NULL
-SELECT * FROM mysql.index_stats;
-db_name	table_name	index_name	prefix_arity	avg_frequency
-test	t1	PRIMARY	1	1.0000
-test	t1	idx3	1	8.5000
-test	t1	idx2	1	7.0000
-test	t1	idx2	2	2.3846
-test	t1	idx1	1	NULL
-test	t1	idx1	2	NULL
-test	t1	idx4	1	6.2000
-test	t1	idx4	2	NULL
-test	t1	idx4	3	NULL
 DELETE FROM mysql.table_stats;
 DELETE FROM mysql.column_stats;
 DELETE FROM mysql.index_stats;

mysql-test/t/mdev-504.test

+--disable_ps_protocol
+
 CREATE TABLE A (
   pk INTEGER AUTO_INCREMENT PRIMARY KEY,
   fdate DATE

mysql-test/t/statistics.test

@@ -368,22 +368,60 @@ SELECT * FROM mysql.table_stats;
 SELECT * FROM mysql.column_stats;
 SELECT * FROM mysql.index_stats;
 
-
 CREATE TABLE t2 LIKE t1;
 ALTER TABLE t2 ENGINE=InnoDB;
 INSERT INTO t2 SELECT * FROM t1;
 
+set optimizer_switch='extended_keys=off';
+
 ANALYZE TABLE t2;
 
 SELECT * FROM mysql.table_stats;
 SELECT * FROM mysql.column_stats ORDER BY column_name;
 SELECT * FROM mysql.index_stats ORDER BY index_name, prefix_arity, table_name;
 
-
 DELETE FROM mysql.table_stats;
 DELETE FROM mysql.column_stats;
 DELETE FROM mysql.index_stats;
 
+set optimizer_switch='extended_keys=on';
+
+ANALYZE TABLE t2;
+
+SELECT * FROM mysql.table_stats;
+SELECT * FROM mysql.column_stats ORDER BY column_name;
+SELECT * FROM mysql.index_stats ORDER BY index_name, prefix_arity, table_name;
+
+ALTER TABLE t2 DROP PRIMARY KEY, DROP INDEX idx1;
+SELECT * FROM mysql.index_stats ORDER BY index_name, prefix_arity, table_name;
+
+UPDATE t2 SET b=0 WHERE b IS NULL;
+ALTER TABLE t2 ADD PRIMARY KEY (a,b);
+SELECT * FROM mysql.index_stats ORDER BY index_name, prefix_arity, table_name;
+
+ANALYZE TABLE t2 PERSISTENT FOR COLUMNS() INDEXES ALL;
+SELECT * FROM mysql.index_stats ORDER BY index_name, prefix_arity, table_name;
+
+ALTER TABLE t2 CHANGE COLUMN b b varchar(30);
+SELECT * FROM mysql.index_stats ORDER BY index_name, prefix_arity, table_name;
+
+ANALYZE TABLE t2 PERSISTENT FOR COLUMNS ALL INDEXES ALL;
+SELECT * FROM mysql.index_stats ORDER BY index_name, prefix_arity, table_name;
+
+ALTER TABLE t2 CHANGE COLUMN b b varchar(32);
+SELECT * FROM mysql.index_stats ORDER BY index_name, prefix_arity, table_name;
+
+ANALYZE TABLE t2 PERSISTENT FOR COLUMNS ALL INDEXES ALL;
+SELECT * FROM mysql.index_stats ORDER BY index_name, prefix_arity, table_name;
+
+ALTER TABLE t2 DROP COLUMN b;
+SELECT * FROM mysql.index_stats ORDER BY index_name, prefix_arity, table_name;
+
+ANALYZE TABLE t2 PERSISTENT FOR COLUMNS() INDEXES ALL;
+SELECT * FROM mysql.index_stats ORDER BY index_name, prefix_arity, table_name;
+
+set optimizer_switch='extended_keys=off';
+
 ALTER TABLE t1
   DROP INDEX idx1,
   DROP INDEX idx4;
@@ -392,6 +430,9 @@ ALTER TABLE t1
   ADD INDEX idx1 (b(4), e), 
   ADD INDEX idx4 (e, b(4), d);
   
+SELECT * FROM mysql.column_stats;
+SELECT * FROM mysql.index_stats;
+
 ANALYZE TABLE t1;
 
 SELECT * FROM mysql.column_stats;
@@ -411,7 +452,6 @@ SELECT * FROM mysql.index_stats;
 
 set use_stat_tables='never';  
 
-
 ANALYZE TABLE t1 PERSISTENT FOR ALL;
 
 SELECT * FROM mysql.table_stats;
@@ -419,11 +459,6 @@ SELECT * FROM mysql.column_stats;
 SELECT * FROM mysql.index_stats;
 
 
-SELECT * FROM mysql.table_stats;
-SELECT * FROM mysql.column_stats;
-SELECT * FROM mysql.index_stats;
-
-
 DELETE FROM mysql.table_stats;
 DELETE FROM mysql.column_stats;
 DELETE FROM mysql.index_stats;

sql/sql_base.h

@@ -321,7 +321,8 @@ int alloc_statistics_for_table(THD *thd, TABLE *table);
 int update_statistics_for_table(THD *thd, TABLE *table);
 int delete_statistics_for_table(THD *thd, LEX_STRING *db, LEX_STRING *tab);
 int delete_statistics_for_column(THD *thd, TABLE *tab, Field *col);
-int delete_statistics_for_index(THD *thd, TABLE *tab, KEY *key_info);
+int delete_statistics_for_index(THD *thd, TABLE *tab, KEY *key_info,
+                                bool ext_prefixes_only);
 int rename_table_in_stat_tables(THD *thd, LEX_STRING *db, LEX_STRING *tab,
                                 LEX_STRING *new_db, LEX_STRING *new_tab);
 int rename_column_in_stat_tables(THD *thd, TABLE *tab, Field *col,

sql/sql_statistics.cc

@@ -2660,6 +2660,9 @@ int delete_statistics_for_column(THD *thd, TABLE *tab, Field *col)
   tab         The table the index belongs to
   @param
   key_info    The descriptor of the index whose statistics is to be deleted
+  @param
+  ext_prefixes_only  Delete statistics only on the index prefixes extended by
+                     the components of the primary key 
 
   @details
   The function delete statistics on the index  specified by 'key_info'
@@ -2675,7 +2678,8 @@ int delete_statistics_for_column(THD *thd, TABLE *tab, Field *col)
    definition of a column used in the definition of the index. 
 */
 
-int delete_statistics_for_index(THD *thd, TABLE *tab, KEY *key_info)
+int delete_statistics_for_index(THD *thd, TABLE *tab, KEY *key_info,
+                                bool ext_prefixes_only)
 {
   int err;
   bool save_binlog_row_based;
@@ -2702,14 +2706,29 @@ int delete_statistics_for_index(THD *thd, TABLE *tab, KEY *key_info)
 
   stat_table= tables.table;
   Index_stat index_stat(stat_table, tab);
-  index_stat.set_index_prefix_key_fields(key_info);
-  while (index_stat.find_next_stat_for_prefix(3))
+  if (!ext_prefixes_only)
   {
-    err= index_stat.delete_stat();
-    if (err && !rc)
-      rc= 1;
+    index_stat.set_index_prefix_key_fields(key_info);
+    while (index_stat.find_next_stat_for_prefix(3))
+    {
+      err= index_stat.delete_stat();
+      if (err && !rc)
+        rc= 1;
+    }
+  }
+  else
+  {
+    for (uint i= key_info->key_parts; i < key_info->ext_key_parts; i++)
+    {
+      index_stat.set_key_fields(key_info, i+1);
+      if (index_stat.find_next_stat_for_prefix(4))
+      {
+        err= index_stat.delete_stat();
+        if (err && !rc)
+          rc= 1;
+      }
+    }
   }
-
   if (save_binlog_row_based)
     thd->set_current_stmt_binlog_format_row();
 

sql/sql_table.cc

@@ -5243,6 +5243,26 @@ mysql_compare_tables(TABLE *table,
     /* Evaluate changes bitmap and send to check_if_incompatible_data() */
     if (!(tmp= field->is_equal(tmp_new_field)))
     {
+      if (table->s->tmp_table == NO_TMP_TABLE)
+      {
+        KEY *key_info= table->key_info; 
+	for (uint i=0; i < table->s->keys; i++, key_info++)
+	{
+          if (field->part_of_key.is_set(i))
+	  {
+            uint key_parts= table->actual_n_key_parts(key_info);
+            for (uint j= 0; j < key_parts; j++)
+	    {
+              if (key_info->key_part[j].fieldnr-1 == field->field_index)
+	      {
+                (void) delete_statistics_for_index(thd, table, key_info,
+                                                   j >= key_info->key_parts);
+                break;
+	      }
+            }           
+          }
+        }      
+      }
       DBUG_PRINT("info", ("!field_is_equal('%s') -> ALTER_TABLE_DATA_CHANGED",
                           new_field->field_name));
       DBUG_RETURN(0);
@@ -5342,7 +5362,20 @@ mysql_compare_tables(TABLE *table,
       field->flags|= FIELD_IN_ADD_INDEX;
     }
     if (table->s->tmp_table == NO_TMP_TABLE)
-      (void) delete_statistics_for_index(thd, table, table_key);
+    {
+      (void) delete_statistics_for_index(thd, table, table_key, FALSE);
+      if (table_key - table->key_info == table->s->primary_key)
+      {
+        KEY *tab_key_info= table->key_info;
+	for (uint j=0; j < table->s->keys; j++, tab_key_info++)
+	{
+          if (tab_key_info->key_parts != tab_key_info->ext_key_parts)
+	    (void) delete_statistics_for_index(thd, table, tab_key_info,
+                                               TRUE);
+	}
+      }
+    }
+
     DBUG_PRINT("info", ("index changed: '%s'", table_key->name));
   }
   /*end of for (; table_key < table_key_end;) */
@@ -5544,6 +5577,7 @@ mysql_prepare_alter_table(THD *thd, TABLE *table,
   uint used_fields= create_info->used_fields;
   KEY *key_info=table->key_info;
   bool rc= TRUE;
+  bool modified_primary_key= FALSE;
   Create_field *def;
   Field **f_ptr,*field;
   DBUG_ENTER("mysql_prepare_alter_table");
@@ -5740,7 +5774,7 @@ mysql_prepare_alter_table(THD *thd, TABLE *table,
     Collect all keys which isn't in drop list. Add only those
     for which some fields exists.
   */
-
+ 
   for (uint i=0 ; i < table->s->keys ; i++,key_info++)
   {
     char *key_name= key_info->name;
@@ -5755,7 +5789,19 @@ mysql_prepare_alter_table(THD *thd, TABLE *table,
     if (drop)
     {
       if (table->s->tmp_table == NO_TMP_TABLE)
-        (void) delete_statistics_for_index(thd, table, key_info);
+      {
+        (void) delete_statistics_for_index(thd, table, key_info, FALSE);
+        if (i == table->s->primary_key)
+	{
+          KEY *tab_key_info= table->key_info;
+	  for (uint j=0; j < table->s->keys; j++, tab_key_info++)
+	  {
+            if (tab_key_info->key_parts != tab_key_info->ext_key_parts)
+	      (void) delete_statistics_for_index(thd, table, tab_key_info,
+                                                 TRUE);
+	  }
+	}
+      }  
       drop_it.remove();
       continue;
     }
@@ -5786,6 +5832,8 @@ mysql_prepare_alter_table(THD *thd, TABLE *table,
       }
       if (!cfield)
       {
+        if (table->s->primary_key == i)
+          modified_primary_key= TRUE;
         delete_index_stat= TRUE;
 	continue;				// Field is removed
       }
@@ -5830,8 +5878,15 @@ mysql_prepare_alter_table(THD *thd, TABLE *table,
                                             strlen(cfield->field_name),
 					    key_part_length));
     }
-    if (delete_index_stat && table->s->tmp_table == NO_TMP_TABLE)
-      (void) delete_statistics_for_index(thd, table, key_info);
+    if (table->s->tmp_table == NO_TMP_TABLE)
+    {
+      if (delete_index_stat) 
+        (void) delete_statistics_for_index(thd, table, key_info, FALSE);
+      else if (modified_primary_key &&
+               key_info->key_parts != key_info->ext_key_parts)
+        (void) delete_statistics_for_index(thd, table, key_info, TRUE);
+    }
+
     if (key_parts.elements)
     {
       KEY_CREATE_INFO key_create_info;