Possible fix for CI issue 2406

gistfile1.txt

diff --git a/system/database/DB_query_builder.php b/system/database/DB_query_builder.php
index 292621b..569490e 100644
--- a/system/database/DB_query_builder.php
+++ b/system/database/DB_query_builder.php
@@ -2554,7 +2554,7 @@ abstract class CI_DB_query_builder extends CI_DB_driver {
 			{
 				continue;
 			}
-			$this->$qb_variable = array_merge($this->$qb_variable, array_diff($this->$qb_cache_var, $this->$qb_variable));
+			$this->$qb_variable = array_merge($this->$qb_variable, array_udiff($this->$qb_cache_var, $this->$qb_variable, '_ci_array_diff'));
 		}
 
 		// If we are "protecting identifiers" we need to examine the "from"
@@ -2679,5 +2679,36 @@ abstract class CI_DB_query_builder extends CI_DB_driver {
 
 }
 
+// --------------------------------------------------------------------
+
+if ( ! function_exists('_ci_array_diff'))
+{
+	/**
+	 * An alternative to the native array_diff() function
+	 * that can also compare multi-dimensional arrays and is
+	 * intended to be used with array_udiff() only.
+	 *
+	 * @deprecated	3.0.0	Replace its usage with a lambda function
+	 *			when PHP 5.3 becomes the minimum requirement.
+	 *
+	 * @param	mixed	$value1
+	 * @param	mixed	$value2
+	 * @return	int
+	 */
+	function _ci_array_diff($value1, $value2)
+	{
+		if ($value1 === $value2)
+		{
+			return 0;
+		}
+		elseif ($value1 > $value2)
+		{
+			return 1;
+		}
+
+		return -1;
+	}
+}
+
 /* End of file DB_query_builder.php */
 /* Location: ./system/database/DB_query_builder.php */
\ No newline at end of file

New values should be appended, e.g. any new where clause should come after any cached values.

// $this->$qb_variable = 
//      array_merge(
//           $this->$qb_variable, 
//           array_udiff(
//                  $this->$qb_cache_var, 
//                  $this->$qb_variable, 
//                  '_ci_array_diff'
//              )
//         );

$this->$qb_variable = 
    array_merge(
        $this->$qb_cache_var,
        array_udiff(
            $this->$qb_variable,
            $this->$qb_cache_var, 
            '_ci_array_diff'
        )
    );

You can test with the following, where the or_where would otherwise be placed before the other where clauses, causing an mysql error.

$this->output->enable_profiler(TRUE);

$this->db->start_cache();

$foo = $this->db
  ->select('id, title')
  ->from('pages')
  ->where('id', 2)
  ->or_where('id', 3);

$this->db->stop_cache();

echo $foo->count_all_results();

$foo->or_where('id', 4);

var_dump( $foo->get()->result() );