Update Query Rewriter comments

lib/cartodb/utils/overviews_query_rewriter.js

@@ -213,24 +213,24 @@ function overview_table_for_zoom_level(table_overviews, zoom_level) {
 }
 
 // Transform an SQL query so that it uses overviews.
-// overviews contains metadata about the overviews to be used:
-//     { 'table-name': {1: { table: 'overview-table-1' }, ... }, ... }
 //
 // For a given query `SELECT * FROM table`,  if any of tables in it
 // has overviews as defined by the provided metadat, the query will
 // be transform into something similar to this:
 //
 //     WITH _vovw_scale AS ( ... ), -- define scale level
-//     WITH _vovw_table AS ( ... ), -- define union of overviews and base table
-//     SELECT * FROM _vovw_table -- query with table replaced by _vovw_table
+//     SELECT * FROM                -- in the query the table is replaced by:
+//      ( ... ) AS _vovw_table      -- a union of overviews and base table
 //
-// This transformation can in principle be applied to arbitrary queries
-// (except for the case of queries that include the name of tables with
-// overviews inside text literals: at the current table name substitution
-// doesnn't prevent substitution inside literals).
-// But the transformation will currently only be applied to simple queries
-// of the form detected by the overviews_supported_query function.
-// TODO: document recent changes (zoom_level option, filters...)
+// The data argument has the form:
+//    {
+//        overviews:             // overview tables metadata
+//             { 'table-name': {1: { table: 'overview-table-1' }, ... }, ... },
+//        zoom_level: ...,       // optional zoom level
+//        filters: ...,          // filters definition
+//        unfiltered_query: ..., // query without the filters
+//        bbox_filter: ...       // bounding-box filter
+//    }
 OverviewsQueryRewriter.prototype.query = function(query, data, options) {
     options = options || {};
 
@@ -258,11 +258,6 @@ OverviewsQueryRewriter.prototype.query = function(query, data, options) {
         // could not or didn't need to alter the query
         rewritten_query = query;
     } else {
-        // TODO: determine if overviews can be used for the filters.
-        // Otherwise use the base table.
-        // Applicability of the filters should depend both on the expected
-        // row count of the result and on the columns to be filter and the
-        // way they're agregated in overviews.
         rewritten_query = apply_filters_to_query(rewritten_query, filters, bbox_filter);
     }