replaced 'LIMIT 0' by 'WHERE 0=1' (fixes #13731)

python/plugins/db_manager/db_plugins/oracle/TODO.md

@@ -3,10 +3,6 @@
 * SQL Window - "Retrieve columns" don't work => problem in
   dlg_sql_window.py (not enough abstraction for connectors). 
 
-* SQL Window - Can't retrieve column: dlg_sql_window.py launch an
-  invalid request for Oracle (no LIMIT operator in Oracle). Should
-  patch dlg_sql_window.py to use a connector method to grab columns.
-
 * Query-builder - Add date functions menu (needs to change the main
   code of query builder).
 

python/plugins/db_manager/dlg_sql_window.py

@@ -287,7 +287,7 @@ def fillColumnCombos(self):
         cols = []
         quotedCols = []
         connector = self.db.connector
-        sql = u"SELECT * FROM (%s\n) AS %s LIMIT 0" % (unicode(query), connector.quoteId(alias))
+        sql = u"SELECT * FROM (%s\n) AS %s WHERE 0=1" % (unicode(query), connector.quoteId(alias))
 
         c = None
         try: