Rebuild SQLServerPlatform::doModifyLimitQuery again to use a CTE and only 1 regex.

* fix tests to use new CTE-based method

lib/Doctrine/DBAL/Platforms/SQLServerPlatform.php

@@ -1182,77 +1182,63 @@ class SQLServerPlatform extends AbstractPlatform
 
         $start   = $offset + 1;
         $end     = $offset + $limit;
-        $orderBy = stristr($query, 'ORDER BY');
 
-        //Remove ORDER BY from $query (including nested parentheses in order by list).
-        $query = preg_replace('/\s+ORDER\s+BY\s+([^()]+|\((?:(?:(?>[^()]+)|(?R))*)\))+/i', '', $query);
-
-        $format  = 'SELECT * FROM (%s) AS doctrine_tbl WHERE doctrine_rownum BETWEEN %d AND %d ORDER BY doctrine_rownum';
-
-        // Pattern to match "main" SELECT ... FROM clause (including nested parentheses in select list).
-        $selectFromPattern = '/^(\s*SELECT\s+(?:(.*)(?![^(]*\))))\sFROM\s/i';
-
-        if ( ! $orderBy) {
-            //Replace only "main" FROM with OVER to prevent changing FROM also in subqueries.
-            $query = preg_replace(
-                $selectFromPattern,
-                '$1, ROW_NUMBER() OVER (ORDER BY (SELECT 0)) AS doctrine_rownum FROM ',
-                $query,
-                1
-            );
-
-            return sprintf($format, $query, $start, $end);
-        }
-
-        //Clear ORDER BY
-        $orderBy        = preg_replace('/ORDER\s+BY\s+(.*)/i', '$1', $orderBy);
-        $orderByParts   = explode(',', $orderBy);
-        $orderByColumns = array();
-
-        //Split ORDER BY into parts
-        foreach ($orderByParts as &$part) {
-
-            if (preg_match('/(([^\s]*)\.)?([^\.\s]*)\s*(ASC|DESC)?/i', trim($part), $matches)) {
-                $orderByColumns[] = array(
-                    'column'    => $matches[3],
-                    'hasTable'  => ( ! empty($matches[2])),
-                    'sort'      => isset($matches[4]) ? $matches[4] : null,
-                    'table'     => empty($matches[2]) ? '[^\.\s]*' : $matches[2]
-                );
-            }
+        // We'll find a SELECT or SELECT distinct and append 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.
+        $selectPattern = '/^(\s*SELECT\s+(?:DISTINCT|)\s*)(.*)$/i';
+        $replacePattern = sprintf('$1%s $2', "TOP $end");
+        $query = preg_replace($selectPattern, $replacePattern, $query);
+
+        if (stristr($query, "ORDER BY")) {
+            // Inner order by is not valid in SQL Server for our purposes
+            // TODO throw DBALException here?
+            $query = $this->scrubInnerOrderBy($query);
         }
 
-        $isWrapped = (preg_match('/SELECT DISTINCT .* FROM \(.*\) dctrn_result/', $query)) ? true : false;
-
-        $overColumns = array();
-
-        //Find alias for each column used in ORDER BY
-        if ( ! empty($orderByColumns)) {
-            foreach ($orderByColumns as $column) {
-                $pattern = sprintf('/%s\.%s\s+(?:AS\s+)?([^,\s)]+)/i', $column['table'], $column['column']);
-
-                if ($isWrapped) {
-                    $overColumn = preg_match($pattern, $query, $matches)
-                        ? $matches[1] : '';
-                } else {
-                    $overColumn = preg_match($pattern, $query, $matches)
-                        ? ($column['hasTable'] ? $column['table']  . '.' : '') . $column['column']
-                        : $column['column'];
-                }
+        // Build a new limited query around the original, using a CTE
+        return sprintf(
+            "WITH dctrn_cte AS (%s) "
+            . "SELECT * FROM ("
+            . "SELECT *, ROW_NUMBER() OVER (ORDER BY (SELECT 0)) AS doctrine_rownum FROM dctrn_cte"
+            . ") AS doctrine_tbl "
+            . "WHERE doctrine_rownum BETWEEN %d AND %d ORDER BY doctrine_rownum ASC",
+            $query,
+            $start,
+            $end
+        );
+    }
 
-                if (isset($column['sort'])) {
-                    $overColumn .= ' ' . $column['sort'];
+    /**
+     * Remove ORDER BY clauses in subqueries - they're not supported by SQL Server.
+     *
+     * @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");
+        while ($count-- > 0) {
+            $qLen = strlen($query);
+            $orderByPos = stripos($query, " ORDER BY");
+            $parenCount = 0;
+            $currentPosition = $orderByPos;
+            while ($parenCount >= 0 && $currentPosition < $qLen) {
+                if ($query[$currentPosition] == '(') {
+                    $parenCount++;
+                } elseif ($query[$currentPosition] == ')') {
+                    $parenCount--;
                 }
 
-                $overColumns[] = $overColumn;
+                $currentPosition++;
+            }
+            if ($currentPosition < $qLen - 1) {
+                $query = substr($query, 0, $orderByPos) . substr($query, $currentPosition - 1);
             }
         }
-
-        //Replace only first occurrence of FROM with $over to prevent changing FROM also in subqueries.
-        $over  = 'ORDER BY ' . implode(', ', $overColumns);
-        $query = preg_replace($selectFromPattern, "$1, ROW_NUMBER() OVER ($over) AS doctrine_rownum FROM ", $query, 1);
-
-        return sprintf($format, $query, $start, $end);
+        return $query;
     }
 
     /**