diff --git a/src/pg/sql/42_observatory_exploration.sql b/src/pg/sql/42_observatory_exploration.sql
index c4f0853..d95662a 100644
--- a/src/pg/sql/42_observatory_exploration.sql
+++ b/src/pg/sql/42_observatory_exploration.sql
@@ -2,29 +2,43 @@
 -- return a table that contains a string match based on input
 -- TODO: implement search for timespan
 
-CREATE OR REPLACE FUNCTION OBS_SearchTables(
+CREATE OR REPLACE FUNCTION _OBS_SearchTables(
   search_term text,
-  time_span text DEFAULT '2009 - 2013'
+  time_span text DEFAULT NULL
 )
-RETURNS text[]
+RETURNS table(tablename text, timespan text)
 As $$
 DECLARE
   out_var text[];
 BEGIN
 
-  EXECUTE
-  'SELECT array_agg(tablename)
-     FROM observatory.obs_table t
-     JOIN observatory.obs_column_table ct
-       ON ct.table_id = t.id
-     JOIN observatory.obs_column c
-       ON ct.column_id = c.id
-     WHERE c.type ILIKE ''geometry''
-      AND c.id = $1'
-  INTO out_var
-  USING search_term;
-
-  RETURN out_var;
+  IF time_span IS NULL
+  THEN
+    RETURN QUERY
+    EXECUTE
+    'SELECT tablename, timespan
+       FROM observatory.obs_table t
+       JOIN observatory.obs_column_table ct
+         ON ct.table_id = t.id
+       JOIN observatory.obs_column c
+         ON ct.column_id = c.id
+       WHERE c.type ILIKE ''geometry''
+        AND c.id = $1'
+    USING search_term;
+  ELSE
+    RETURN QUERY
+    EXECUTE
+    'SELECT tablename, timespan
+       FROM observatory.obs_table t
+       JOIN observatory.obs_column_table ct
+         ON ct.table_id = t.id
+       JOIN observatory.obs_column c
+         ON ct.column_id = c.id
+       WHERE c.type ILIKE ''geometry''
+        AND c.id = $1
+        AND t.timespan = $2'
+    USING search_term, time_span;
+  END IF;
 
 END;
-$$ LANGUAGE plpgsql;
+$$ LANGUAGE plpgsql IMMUTABLE;