Fix for bug #2628 "ALTER TABLE destroys table and reports success"

BitKeeper/etc/logging_ok

@@ -12,6 +12,7 @@ heikki@donna.mysql.fi
 heikki@hundin.mysql.fi
 jani@hynda.mysql.fi
 jorge@linux.jorge.mysql.com
+konstantin@mysql.com
 lenz@mysql.com
 miguel@hegel.(none)
 miguel@hegel.br

mysql-test/r/alter_table.result

@@ -32,3 +32,11 @@ i
 2
 3
 4
+name
+current
+name
+mysqltest
+name
+current
+name
+mysqltest

mysql-test/t/alter_table.test

@@ -82,3 +82,20 @@ alter table t1 drop i,add i int unsigned not null auto_increment, drop primary k
 select * from t1;
 drop table t1;
 
+#
+# Bug #2628: 'alter table t1 rename mysqltest.t1' silently drops mysqltest.t1 
+# if it exists
+#
+create table t1 (name char(15));
+insert into t1 (name) values ("current");
+create database mysqltest;
+create table mysqltest.t1 (name char(15));
+insert into mysqltest.t1 (name) values ("mysqltest");
+select * from t1;
+select * from mysqltest.t1;
+--error 1050
+alter table t1 rename mysqltest.t1;
+select * from t1;
+select * from mysqltest.t1;
+drop table t1;
+drop database mysqltest;

sql/sql_table.cc

@@ -1151,7 +1151,7 @@ int mysql_alter_table(THD *thd,char *new_db, char *new_name,
   thd->proc_info="init";
   table_name=table_list->real_name;
   db=table_list->db;
-  if (!new_db)
+  if (!new_db || !strcmp(new_db, db))
     new_db=db;
 
   if (!(table=open_ltable(thd,table_list,TL_WRITE_ALLOW_READ)))
@@ -1161,14 +1161,20 @@ int mysql_alter_table(THD *thd,char *new_db, char *new_name,
   if (new_name)
   {
     strmov(new_name_buff,new_name);
-    fn_same(new_name_buff,table_name,3);
     if (lower_case_table_names)
       casedn_str(new_name);
-    if ((lower_case_table_names &&
-	 !my_strcasecmp(new_name_buff,table_name)) ||
-	(!lower_case_table_names &&
+    if (new_db == db &&
+        (lower_case_table_names &&
+	 !my_strcasecmp(new_name_buff,table_name) ||
+	 !lower_case_table_names &&
 	 !strcmp(new_name_buff,table_name)))
-      new_name=table_name;			// No. Make later check easier
+    {
+      /*
+        Source and destination table names are equal: make later check
+        easier.
+      */
+      new_name= table_name;
+    }
     else
     {
       if (table->tmp_table)