- improved an optimization, to produce a simpler select condition under certain circumstances

git-svn-id: http://galileo.dmi.unict.it/svn/relational/trunk@343 014f5005-505e-4b48-8d0a-63407b615a7c

CHANGELOG

@@ -1,6 +1,7 @@
 1.2
 - Better tokenizer, gives more indicative errors
 - Parser gives more indicative errors
+- Improved select_union_intersect_subtract optimization to avoid parenthesis whenever possible
 
 1.1
 - Incorrect relational operations now raise an exception instead of returning None

relational/optimizations.py

@@ -475,7 +475,22 @@ def select_union_intersect_subtract(n):
         
         newnode=parser.node()
         
-        newnode.prop='((%s) %s (%s))' % (n.left.prop,op,n.right.prop)
+        if n.left.prop.startswith('(') or n.right.prop.startswith('('):
+            t_str='('
+            if n.left.prop.startswith('('):
+                t_str+='(%s)'
+            else:
+                t_str+='%s'
+            t_str+=' %s '
+            if n.right.prop.startswith('('):
+                t_str+='(%s)'
+            else:
+                t_str+='%s'
+            t_str+=')'
+            
+            newnode.prop= t_str % (n.left.prop,op,n.right.prop)
+        else:
+            newnode.prop='%s %s %s' % (n.left.prop,op,n.right.prop)
         newnode.name=SELECTION
         newnode.child=n.left.child
         newnode.kind=parser.UNARY

test/select_join_opt.query

@@ -0,0 +1 @@
+σ skill=='C' and chief==0 ((σ age<30 (people) ᑌ σ age>40(people)) ᐅᐊ skills)

test/select_join_opt.result

@@ -0,0 +1,3 @@
+id,name,chief,age,skill
+0,jack,0,22,C
+4,eve,0,25,C