* Format DATE_SUB and DATEFIFF for dm.

lib/dbh/dbh.class.php

@@ -381,6 +381,8 @@ class dbh
             case 'dm':
                 /* DATE convert to TO_CHAR. */
                 $sql = preg_replace("/\bDATE\(([^)]*)\)/",  "TO_CHAR($1, 'yyyy-mm-dd')", $sql, -1);
+                $sql = $this->formatDmDateSubFunction($sql);
+                $sql = $this->formatDmDateDiffFunction($sql);
 
                 return $sql;
 
@@ -417,6 +419,37 @@ class dbh
         return $field;
     }
 
+    /**
+     * Format DATE_SUB function of dmdb.
+     *
+     * @param  string $sql
+     * @access public
+     * @return string
+     *
+     * DATE_SUB(t1.today, INTERVAL TIMESTAMPDIFF(YEAR, t1.firstDay, t1.today) YEAR) -> DATEADD(YEAR, -DATEDIFF(YEAR, t1.firstDay, t1.today), t1.today)
+     */
+    public function formatDmDateSubFunction($sql)
+    {
+        $pattern = "/DATE_SUB\((.*),\s*INTERVAL\s*(.*)\s*YEAR\)/";
+        preg_match($pattern, $sql, $matches);
+
+        return count($matches) == 0 ? $sql : preg_replace($pattern, "DATEADD(YEAR, -DATEDIFF(YEAR, \\2, \\1), \\1)", $sql);
+    }
+
+    /**
+     * Format DATEDIFF function of dmdb.
+     *
+     * @param  string $sql
+     * @access public
+     * @return string
+     *
+     * DATEDIFF(date1,date2) -> DATEDIFF(DD,date1,date2)
+     */
+    public function formatDmDateDiffFunction($sql)
+    {
+        return preg_replace('/DATEDIFF\(/', 'DATEDIFF(DD,', $sql);
+    }
+
     /**
      * Format attribute of field.
      *