stub for swap_rename_select

git-svn-id: http://galileo.dmi.unict.it/svn/relational/trunk@160 014f5005-505e-4b48-8d0a-63407b615a7c

relational/optimizations.py

@@ -168,5 +168,19 @@ def subsequent_renames(n):
         changes+=subsequent_renames(n.left)
     return changes
 
+def swap_rename_select(n):
+    '''This function locates things like σ k(ρ j(R)) and replaces
+    them with ρ j(σ k(R)). Renaming the attributes used in the
+    selection, so the operation is still valid.'''
+    #TODO document into the wiki
+    changes=0
+    
+    #recoursive scan
+    if n.kind==optimizer.UNARY:        
+        changes+=swap_rename_select(n.child)
+    elif n.kind==optimizer.BINARY:
+        changes+=swap_rename_select(n.right)
+        changes+=swap_rename_select(n.left)
+    return changes
 
-general_optimizations=[duplicated_select,down_to_unions_subtractions_intersections,duplicated_projection,selection_inside_projection,subsequent_renames]
+general_optimizations=[duplicated_select,down_to_unions_subtractions_intersections,duplicated_projection,selection_inside_projection,subsequent_renames,swap_rename_select]

relational/optimizer.py

@@ -194,8 +194,8 @@ if __name__=="__main__":
     #a=tokenize("(a-b*c)*(b-c)")
     #print tree("σ i==2 (c ᑌ d - (aᑎb))") == tree("σ i==3 (c ᑌ d - (aᑎb))")
         
-    a=general_optimize("ρ age➡a,cognome➡cogn(ρ ciccio➡age,nome➡nom(R))")
+    a=general_optimize("σ age==3(ρ ciccio➡age,nome➡nom(R))")
     #a=general_optimize("σ i==2 (σ b>5 (d))")
-    print '=========',a
+    print a
     #print node(a)
     #print tokenize("(a)")