a fix (bug #2361: ALTER TABLE ... DROP PRIMARY KEY drops a non-primary key).

mysql-test/r/alter_table.result

@@ -412,3 +412,12 @@ t1	0	PRIMARY	1	Host	A	NULL	NULL	NULL		BTREE
 t1	0	PRIMARY	2	User	A	0	NULL	NULL		BTREE	
 t1	1	Host	1	Host	A	NULL	NULL	NULL		BTREE	disabled
 DROP TABLE t1;
+CREATE TABLE t1 (a int UNIQUE);
+ALTER TABLE t1 DROP PRIMARY KEY;
+SHOW CREATE TABLE t1;
+Table	Create Table
+t1	CREATE TABLE `t1` (
+  `a` int(11) default NULL,
+  UNIQUE KEY `a` (`a`)
+) ENGINE=MyISAM DEFAULT CHARSET=latin1
+DROP TABLE t1;

mysql-test/t/alter_table.test

@@ -244,3 +244,12 @@ LOCK TABLES t1 WRITE;
 ALTER TABLE t1 DISABLE KEYS;
 SHOW INDEX FROM t1;
 DROP TABLE t1;
+
+#
+# Bug 2361
+#
+
+CREATE TABLE t1 (a int UNIQUE);
+ALTER TABLE t1 DROP PRIMARY KEY;
+SHOW CREATE TABLE t1;
+DROP TABLE t1;

sql/sql_table.cc

@@ -2242,13 +2242,15 @@ int mysql_alter_table(THD *thd,char *new_db, char *new_name,
   KEY *key_info=table->key_info;
   for (uint i=0 ; i < table->keys ; i++,key_info++)
   {
-    if (drop_primary && (key_info->flags & HA_NOSAME))
+    char *key_name= key_info->name;
+
+    if (drop_primary && !my_strcasecmp(system_charset_info, key_name,
+                                       "PRIMARY"))
     {
-      drop_primary=0;
+      drop_primary= 0;
       continue;
     }
 
-    char *key_name=key_info->name;
     Alter_drop *drop;
     drop_it.rewind();
     while ((drop=drop_it++))