From b3a9d98d24d15806da83f9525ffdba24fc3addfe Mon Sep 17 00:00:00 2001
From: LtWorf <LtWorf@014f5005-505e-4b48-8d0a-63407b615a7c>
Date: Fri, 8 May 2009 14:46:29 +0000
Subject: [PATCH] added selection_inside_projection

git-svn-id: http://galileo.dmi.unict.it/svn/relational/trunk@153 014f5005-505e-4b48-8d0a-63407b615a7c
---
 relational/optimizations.py | 27 +++++++++++++++++++++++++--
 1 file changed, 25 insertions(+), 2 deletions(-)

diff --git a/relational/optimizations.py b/relational/optimizations.py
index ea45533..e8e4a27 100644
--- a/relational/optimizations.py
+++ b/relational/optimizations.py
@@ -78,6 +78,29 @@ def down_to_unions_subtractions_intersections(n):
         changes+=down_to_unions_subtractions_intersections(n.right)
         changes+=down_to_unions_subtractions_intersections(n.left)
     return changes
-    
 
-general_optimizations=[duplicated_select,down_to_unions_subtractions_intersections]
+def duplicated_projection(n):
+    '''This function locates thing like π i ( π j (R)) and replaces
+    them with π i (R)'''
+    changes=0
+    
+    
+    if n.name=='π' and n.child.name=='π':
+        n.child=n.child.child
+        changes+=1
+    
+    #recoursive scan
+    if n.kind==optimizer.UNARY:
+        changes+=duplicated_projection(n.child)
+    elif n.kind==optimizer.BINARY:
+        changes+=duplicated_projection(n.right)
+        changes+=duplicated_projection(n.left)
+    return changes
+
+def selection_inside_projection(n):
+    '''This function locates things like  σ j (π k(R)) and
+    converts them into π k(σ j (R))'''
+    changes=0
+    return changes
+    
+    general_optimizations=[duplicated_select,down_to_unions_subtractions_intersections,duplicated_projection,selection_inside_projection]