rewrite isTableExists for performance reasons (#1720)

faster implementation of isTableExists withous "showtablestatus"

Author: jonashrem

lib/Varien/Db/Adapter/Pdo/Mysql.php

@@ -2630,7 +2630,22 @@ public function truncateTable($tableName, $schemaName = null)
      */
     public function isTableExists($tableName, $schemaName = null)
     {
-        return $this->showTableStatus($tableName, $schemaName) !== false;
+        $fromDbName = 'DATABASE()';
+        if ($schemaName !== null) {
+            $fromDbName = $this->quote($schemaName);
+        }
+
+        $sql = sprintf(
+            'SELECT COUNT(1) AS tbl_exists FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_NAME = %s AND TABLE_SCHEMA = %s',
+            $this->quote($tableName),
+            $fromDbName
+        );
+        $ddl = $this->rawFetchRow($sql, 'tbl_exists');
+        if ($ddl) {
+            return true;
+        }
+
+        return false;
     }
 
     /**