- Implemented select_union_intersect_subtract general optimization

- Added tests for the new optimization



git-svn-id: http://galileo.dmi.unict.it/svn/relational/trunk@268 014f5005-505e-4b48-8d0a-63407b615a7c

CHANGELOG

@@ -11,6 +11,7 @@
 - Fixed futile_union_intersection_subtraction optimization that didn't work when selection operator was in the left subtree (Rev 261)
 - Module parallel does something, can execute queries in parallel
 - Set hash method for the classes
+- Implemented select_union_intersect_subtract general optimization
 
 0.11
 - Font is set only on windows (Rev 206)

relational/optimizations.py

@@ -449,6 +449,27 @@ def swap_rename_select(n):
     
     return changes+recoursive_scan(swap_rename_select,n)
 
+def select_union_intersect_subtract(n):
+    '''This function locates things like σ i(a) ᑌ σ q(a)
+    and replaces them with σ (i OR q) (a)
+    Removing a O² operation like the union'''
+    changes=0
+    if n.name in ('ᑌ', 'ᑎ', '-') and n.left.name=='σ' and n.right.name=='σ' and n.left.child==n.right.child:
+        cahnges=1
+        
+        d={'ᑌ':'or', 'ᑎ':'and', '-':'and not'}
+        op=d[n.name]
+        
+        newnode=parser.node()
+        
+        newnode.prop='((%s) %s (%s))' % (n.left.prop,op,n.right.prop)
+        newnode.name='σ'
+        newnode.child=n.left.child
+        newnode.kind=parser.UNARY
+        replace_node(n,newnode)
+        
+    return changes+recoursive_scan(select_union_intersect_subtract,n)
+
 def selection_and_product(n,rels):
     '''This function locates things like σ k (R*Q) and converts them into
     σ l (σ j (R) * σ i (Q)). Where j contains only attributes belonging to R,
@@ -549,7 +570,7 @@ def selection_and_product(n,rels):
             
     return changes+recoursive_scan(selection_and_product,n,rels)
         
-general_optimizations=[duplicated_select,down_to_unions_subtractions_intersections,duplicated_projection,selection_inside_projection,subsequent_renames,swap_rename_select,futile_union_intersection_subtraction,swap_union_renames,swap_rename_projection]
+general_optimizations=[duplicated_select,down_to_unions_subtractions_intersections,duplicated_projection,selection_inside_projection,subsequent_renames,swap_rename_select,futile_union_intersection_subtraction,swap_union_renames,swap_rename_projection,select_union_intersect_subtract]
 specific_optimizations=[selection_and_product]
 
 if __name__=="__main__":

relational/parser.py

@@ -132,7 +132,7 @@ class node (object):
             
         return '\n'+r
     def get_left_leaf(self):
-        '''This function returns the most left leaf in the tree. It is needed by some optimizations.'''
+        '''This function returns the leftmost leaf in the tree. It is needed by some optimizations.'''
         if self.kind==RELATION:
             return self
         elif self.kind==UNARY:

test/union_and_select.query

@@ -0,0 +1 @@
+σ skill=='C'(skills) ᑎ σ id%2==0 (skills)

test/union_and_select.result

@@ -0,0 +1,4 @@
+id,skill
+0,C
+2,C
+4,C

test/union_not_select.query

@@ -0,0 +1 @@
+σ skill=='C' (skills) - σ id%2==0(skills)

test/union_not_select.result

@@ -0,0 +1,3 @@
+id,skill
+5,C
+7,C

test/union_or_select.query

@@ -0,0 +1 @@
+σ age<21 (people) ᑌ σage >30(people)

test/union_or_select.result

@@ -0,0 +1,3 @@
+id,name,chief,age
+3,dean,1,33
+1,carl,0,20