Index: mysql-5.1-innodb-online-alter/sql/sql_table.cc
===================================================================
--- mysql-5.1-innodb-online-alter.orig/sql/sql_table.cc	2008-01-10 15:47:09.000000000 +0100
+++ mysql-5.1-innodb-online-alter/sql/sql_table.cc	2008-01-10 16:05:33.000000000 +0100
@@ -2988,6 +2988,7 @@ mysql_prepare_create_table(THD *thd, HA_
   if (!unique_key && !primary_key &&
       (file->ha_table_flags() & HA_REQUIRE_PRIMARY_KEY))
   {
+    DBUG_ASSERT(false);
     my_message(ER_REQUIRES_PRIMARY_KEY, ER(ER_REQUIRES_PRIMARY_KEY), MYF(0));
     DBUG_RETURN(TRUE);
   }
@@ -5038,6 +5039,7 @@ err:
       index_drop_count    OUT   The number of elements in the array.
       index_add_buffer    OUT   An array of offsets into key_info_buffer.
       index_add_count     OUT   The number of elements in the array.
+      unique_index_count  OUT   The number of unique indexes in original table.
 
   DESCRIPTION
     'table' (first argument) contains information of the original
@@ -5068,7 +5070,8 @@ compare_tables(TABLE *table,
                enum_alter_table_change_level *need_copy_table,
                KEY **key_info_buffer,
                uint **index_drop_buffer, uint *index_drop_count,
-               uint **index_add_buffer, uint *index_add_count)
+               uint **index_add_buffer, uint *index_add_count,
+               uint *unique_index_count)
 {
   Field **f_ptr, *field;
   uint changes= 0, tmp;
@@ -5220,12 +5223,16 @@ compare_tables(TABLE *table,
   */
   *index_drop_count= 0;
   *index_add_count= 0;
+  *unique_index_count= 0;
   for (table_key= table->key_info; table_key < table_key_end; table_key++)
   {
     KEY_PART_INFO *table_part;
     KEY_PART_INFO *table_part_end= table_key->key_part + table_key->key_parts;
     KEY_PART_INFO *new_part;
 
+    if (table_key->flags & HA_NOSAME)
+      (*unique_index_count)++;
+
     /* Search a new key with the same name. */
     for (new_key= *key_info_buffer; new_key < new_key_end; new_key++)
     {
@@ -5850,12 +5857,14 @@ bool mysql_alter_table(THD *thd,char *ne
   uint index_drop_count;
   uint *index_drop_buffer;
   uint index_add_count;
+  uint unique_index_count;
   uint *index_add_buffer;
   bool committed= 0;
   DBUG_ENTER("mysql_alter_table");
 
   LINT_INIT(index_add_count);
   LINT_INIT(index_drop_count);
+  LINT_INIT(unique_index_count);
   LINT_INIT(index_add_buffer);
   LINT_INIT(index_drop_buffer);
 
@@ -6268,7 +6277,8 @@ view_err:
                        &need_copy_table_res,
                        &key_info_buffer,
                        &index_drop_buffer, &index_drop_count,
-                       &index_add_buffer, &index_add_count))
+                       &index_add_buffer, &index_add_count,
+                       &unique_index_count))
       goto err;
    
     if (need_copy_table == ALTER_TABLE_METADATA_ONLY)
@@ -6302,9 +6312,13 @@ view_err:
       DBUG_PRINT("info", ("index dropped: '%s'", key->name));
       if (key->flags & HA_NOSAME)
       {
-        /* Unique key. Check for "PRIMARY". */
-        if (! my_strcasecmp(system_charset_info,
-                            key->name, primary_key_name))
+        /*
+           Unique key. Check for "PRIMARY"
+           or if dropping last unique key.
+        */
+        if ((! my_strcasecmp(system_charset_info,
+                             key->name, primary_key_name)) ||
+            (unique_index_count == 1))
         {
           /* Primary key. */
           needed_online_flags|=  HA_ONLINE_DROP_PK_INDEX;
@@ -6335,9 +6349,14 @@ view_err:
       DBUG_PRINT("info", ("index added: '%s'", key->name));
       if (key->flags & HA_NOSAME)
       {
-        /* Unique key. Check for "PRIMARY". */
-        if (! my_strcasecmp(system_charset_info,
-                            key->name, primary_key_name))
+        /*
+           Unique key. Check for "PRIMARY"
+           or if adding first unique key
+        */
+        if ((! my_strcasecmp(system_charset_info,
+                             key->name, primary_key_name)) ||
+            (unique_index_count == 0) ||
+            (needed_online_flags & HA_ONLINE_DROP_PK_INDEX))
         {
           /* Primary key. */
           needed_online_flags|=  HA_ONLINE_ADD_PK_INDEX;