[tracker] libtracker-data: Make ASK use the same 'true' and 'false' as xsd:boolean

[Philip Van Hoof <pvanhoof src gnome org>]

commit ad57d8c62aa012e7cad2655e9ee55b7363ae9717
Author: Philip Van Hoof <philip codeminded be>
Date:   Mon Apr 11 13:44:30 2011 +0200

    libtracker-data: Make ASK use the same 'true' and 'false' as xsd:boolean
    
    Fixes NB#245589.

 src/libtracker-data/tracker-sparql-query.vala |    7 ++-----
 1 files changed, 2 insertions(+), 5 deletions(-)
---
diff --git a/src/libtracker-data/tracker-sparql-query.vala b/src/libtracker-data/tracker-sparql-query.vala
index 27dae58..397779e 100644
--- a/src/libtracker-data/tracker-sparql-query.vala
+++ b/src/libtracker-data/tracker-sparql-query.vala
@@ -540,20 +540,17 @@ public class Tracker.Sparql.Query : Object {
 
 		// build SQL
 		var sql = new StringBuilder ();
-		sql.append ("SELECT ");
+		sql.append ("SELECT CASE EXISTS ( ");
 
 		expect (SparqlTokenType.ASK);
 
-		sql.append ("COUNT(1) > 0");
-
 		accept (SparqlTokenType.WHERE);
 
 		context = pattern.translate_group_graph_pattern (pattern_sql);
 
 		// select from results of WHERE clause
-		sql.append (" FROM (");
 		sql.append (pattern_sql.str);
-		sql.append (")");
+		sql.append (" ) WHEN 1 THEN 'true' WHEN 0 THEN 'false' ELSE NULL END");
 
 		context = context.parent_context;