Resolved @todo to allow ORDER BY in TOP N subquery with SQL Server 2008 doModifyLimitQuery

lib/Doctrine/DBAL/Platforms/SQLServerPlatform.php

@@ -1183,7 +1183,7 @@ class SQLServerPlatform extends AbstractPlatform
         $start   = $offset + 1;
         $end     = $offset + $limit;
 
-        // We'll find a SELECT or SELECT distinct and append TOP n to it
+        // We'll find a SELECT or SELECT distinct and prepend TOP n to it
         // Even if the TOP n is very large, the use of a CTE will
         // allow the SQL Server query planner to optimize it so it doesn't
         // actually scan the entire range covered by the TOP clause.
@@ -1193,7 +1193,7 @@ class SQLServerPlatform extends AbstractPlatform
 
         if (stristr($query, "ORDER BY")) {
             // Inner order by is not valid in SQL Server for our purposes
-            // TODO throw DBALException here?
+            // unless it's in a TOP N subquery.
             $query = $this->scrubInnerOrderBy($query);
         }
 
@@ -1212,19 +1212,21 @@ class SQLServerPlatform extends AbstractPlatform
 
     /**
      * Remove ORDER BY clauses in subqueries - they're not supported by SQL Server.
+     * Caveat: will leave ORDER BY in TOP N subqueries.
      *
      * @param $query
      * @return string
      *
-     * @todo allow ORDER BY clauses in subqueries that have TOP n, as that is ok.
      */
     private function scrubInnerOrderBy($query) {
         $count = substr_count(strtoupper($query), "ORDER BY");
+        $offset = 0;
         while ($count-- > 0) {
             $qLen = strlen($query);
-            $orderByPos = stripos($query, " ORDER BY");
+            $orderByPos = stripos($query, " ORDER BY", $offset);
             $parenCount = 0;
             $currentPosition = $orderByPos;
+
             while ($parenCount >= 0 && $currentPosition < $qLen) {
                 if ($query[$currentPosition] == '(') {
                     $parenCount++;
@@ -1234,13 +1236,61 @@ class SQLServerPlatform extends AbstractPlatform
 
                 $currentPosition++;
             }
+
+            if ($this->isOrderByInTopNSubquery($query, $orderByPos)) {
+                // If the order by clause is in a TOP N subquery, do not remove
+                // it and continue iteration from the current position.
+                $offset = $currentPosition;
+                continue;
+            }
+
             if ($currentPosition < $qLen - 1) {
                 $query = substr($query, 0, $orderByPos) . substr($query, $currentPosition - 1);
+                $offset = $orderByPos;
             }
         }
         return $query;
     }
 
+    /**
+     * Check an ORDER BY clause to see if it is in a TOP N query or subquery.
+     *
+     * @param string $query The query
+     * @param int $currentPosition Start position of ORDER BY clause
+     * @return bool true if ORDER BY is in a TOP N query, false otherwise
+     */
+    private function isOrderByInTopNSubquery($query, $currentPosition)
+    {
+        // Grab query text on the same nesting level as the ORDER BY clause we're examining.
+        $subQueryBuffer = '';
+        $parenCount = 0;
+
+        // If $parentCount goes negative, we've exited the subquery we're examining.
+        // If $currentPosition goes negative, we've reached the beginning of the query.
+        while ($parenCount >= 0 && $currentPosition >= 0) {
+            if ($query[$currentPosition] == '(') {
+                $parenCount--;
+            }
+            if ($query[$currentPosition] == ')') {
+                $parenCount++;
+            }
+            if ($parenCount === 0) {
+                // Only yank query text on the same nesting level as the ORDER BY clause.
+                $subQueryBuffer = $query[$currentPosition] . $subQueryBuffer;
+            } else {
+                $subQueryBuffer = " " . $subQueryBuffer;
+            }
+
+            $currentPosition--;
+        }
+
+        if (preg_match('/SELECT\s+TOP\s/', $subQueryBuffer)) {
+            return true;
+        }
+
+        return false;
+    }
+
     /**
      * {@inheritDoc}
      */