Manual transfer of the following changeset into the 5.0.23 release clone:

   1.2525 06/06/30 18:29:27 monty@mysql.com +3 -0
   Reverted wrong bug fix (Bug#11228)

mysql-test/r/key.result

@@ -336,8 +336,16 @@ UNIQUE i1idx (i1),
 UNIQUE i2idx (i2));
 desc t1;
 Field	Type	Null	Key	Default	Extra
-i1	int(11)	NO	UNI		
+i1	int(11)	NO	PRI		
 i2	int(11)	NO	UNI		
+show create table t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `i1` int(11) NOT NULL,
+  `i2` int(11) NOT NULL,
+  UNIQUE KEY `i1idx` (`i1`),
+  UNIQUE KEY `i2idx` (`i2`)
+) ENGINE=MyISAM DEFAULT CHARSET=latin1
 drop table t1;
 create table t1 (
 c1 int,

mysql-test/t/key.test

@@ -334,6 +334,7 @@ create table t1 (
  UNIQUE i1idx (i1),
  UNIQUE i2idx (i2));
 desc t1;
+show create table t1;
 drop table t1;
 
 #

sql/table.cc

@@ -678,6 +678,27 @@ int openfrm(THD *thd, const char *name, const char *alias, uint db_stat,
       if (outparam->key_info[key].flags & HA_FULLTEXT)
 	outparam->key_info[key].algorithm= HA_KEY_ALG_FULLTEXT;
 
+      if (primary_key >= MAX_KEY && (keyinfo->flags & HA_NOSAME))
+      {
+	/*
+	  If the UNIQUE key doesn't have NULL columns and is not a part key
+	  declare this as a primary key.
+	*/
+	primary_key=key;
+	for (i=0 ; i < keyinfo->key_parts ;i++)
+	{
+	  uint fieldnr= key_part[i].fieldnr;
+	  if (!fieldnr ||
+	      outparam->field[fieldnr-1]->null_ptr ||
+	      outparam->field[fieldnr-1]->key_length() !=
+	      key_part[i].length)
+	  {
+	    primary_key=MAX_KEY;		// Can't be used
+	    break;
+	  }
+	}
+      }
+
       for (i=0 ; i < keyinfo->key_parts ; key_part++,i++)
       {
 	if (new_field_pack_flag <= 1)