Thanks for taking the time to report this.  It seems that every database has a different way to accomplish random order.  For example:

MySQL uses ORDER BY RAND()
PostgreSQL uses ORDER BY RANDOM()
Oracle uses a subquery with ORDER BY dbms_random.value
SQL Server users ORDER BY NEWID()

For now, we’ve removed mention of this from the user guide, but if you wanted to add the note on rand() for MySQL databases with the user contributed notes feature, that would be appreciated.

Why not setting a common word for random across all drivers ie ci_random_ugly_name so when users call orderby(‘ci_random_ugly_name’); each driver would parse it its own way and you can still have a unified form of documenting it.

I have all copyrights on ‘ci_random_ugly_name’ so try to come up with a diferent name for it (:

Yup, that is the long term solution.  Someone just needs to code it in, so for now I simply removed it.  If you code it up, I’ll push to use your name

OK, I prepared a first attempt at fixing this based on information gathered from the internet. Testing in the different platforms is still required since I only have a mysql server installed.
Please, someone confirm this works on each supported platform or any problems (and preferrably their fixes) you might find

File system/database/DB_active_record.php
Line 406
+      //Check for random ordering
+      if (strtolower($orderby) == ‘random’)
+      {
+        $orderby = $this->_random();
+      }

File system/database/drivers/mssql/mssql_driver.php
Line 478
+  //——————————————————————————————————
+ +  /**
+    * Order criteria used for random ordering
+    *
+    * @return string
+    */
+  function _random()
+  {
+      return “NEWID()”;
+  }

File system/database/drivers/mysql/mysql_driver.php
Line 485
+  //——————————————————————————————————
+ +  /**
+    * Order criteria used for random ordering
+    *
+    * @return string
+    */
+  function _random()
+  {
+      return “RAND()”;
+  }

File system/database/drivers/mysqli/mysqli_driver.php
Line 475
+  //——————————————————————————————————
+ +  /**
+    * Order criteria used for random ordering
+    *
+    * @return string
+    */
+  function _random()
+  {
+      return “RAND()”;
+  }

File system/database/drivers/oci8/oci8_driver.php
Line 601
+  //——————————————————————————————————
+ +  /**
+    * Order criteria used for random ordering
+    *
+    * @return string
+    */
+  function _random()
+  {
+      return “dbms_random.value”;
+  }

File system/database/drivers/odbc/odbc_driver.php
Line 449
+  //——————————————————————————————————
+ +  /**
+    * Order criteria used for random ordering
+    *
+    * @return string
+    */
+  function _random()
+  {
+      return “RND(”.time().”)”;
+  }

File system/database/drivers/postgre/postgre_driver.php
Line 482
+  //——————————————————————————————————
+ +  /**
+    * Order criteria used for random ordering
+    *
+    * @return string
+    */
+  function _random()
+  {
+      return “RANDOM()”;
+  }

File system/database/drivers/sqlite/sqlite_driver.php
Line 481
+  //——————————————————————————————————
+ +  /**
+    * Order criteria used for random ordering
+    *
+    * @return string
+    */
+  function _random()
+  {
+      return “RANDOM()”;
+  }

I’ve opened a forum thread to keep this bug alive as I personally don’t believe this bug to be really resolved

http://codeigniter.com/forums/viewthread/64145/

A note, ‘random’ has been added into order_by(), and replaces the old ‘RAND()’ keyword.