added 1st optimization

git-svn-id: http://galileo.dmi.unict.it/svn/relational/trunk@135 014f5005-505e-4b48-8d0a-63407b615a7c

relational/optimizations.py

@@ -21,8 +21,22 @@
 The list general_optimizations contains pointers to general functions, so they can be called
 within a cycle.'''
 
-def duplicated_select(n):
-    pass
+import optimizer
 
+def duplicated_select(n):
+    '''This function locates and deletes things like
+    σ a ( σ a(C)) and the ones like σ a ( σ b(C))'''
+    if n.name=='σ' and n.child.name=='σ':        
+        if n.prop != n.child.prop: #Nested but different, joining them
+            n.prop = n.prop + " and " + n.child.prop
+        n.child=n.child.child
+
+    #recoursive scan
+    if n.kind==optimizer.UNARY:
+        duplicated_select(n.child)
+    elif n.kind==optimizer.BINARY:
+        duplicated_select(n.right)
+        duplicated_select(n.left)
+    return n
 
 general_optimizations=[duplicated_select]

relational/optimizer.py

@@ -174,6 +174,7 @@ def general_optimize(expression):
     '''This function performs general optimizations. Means that it will not need to
     know the fields used by the relations'''
     n=tree(expression) #Gets the tree
+    print n
     for i in optimizations.general_optimizations:
         n=i(n) #Performs the optimization
     return n.__str__()
@@ -187,7 +188,7 @@ if __name__=="__main__":
     #a= tokenize("(a - (a ᑌ b) * π a,b (a-b)) - ρ 123 (a)")
     #a= tokenize(u"π a,b (a*b)")
     #a=tokenize("(a-b*c)*(b-c)")
-    a=tokenize("((((((((a)))))))) * b -c ")
+    a=general_optimize("σ b>5 ( σ a>2 (C)) * σ a>2 ( σ a>2 (C))")
     print a
-    print node(a)
+    #print node(a)
     #print tokenize("(a)")