- Fixed optimization involving selection and parenthesis in the expression

- Added more clear documentation in recoursive_scan



git-svn-id: http://galileo.dmi.unict.it/svn/relational/trunk@260 014f5005-505e-4b48-8d0a-63407b615a7c

CHANGELOG

@@ -7,6 +7,7 @@
 - Rename will mark the resulting relation as readonly and subsequent updates, insert, updates or deletes will actually copy the content
 - Added testsuite
 - Fixed python expression tokenization, now uses native tokenizer
+- Fixed optimization involving selection and parenthesis in the expression (Rev 260)
 
 0.11
 - Font is set only on windows (Rev 206)
@@ -18,7 +19,7 @@
 - Added .desktop file on svn (Rev 216)
 - Automatically fills some fields in the survey (Rev 217)
 - When a query fails, shows the message of the exception (Rev220)
-- Improved tokenizer for select in optimizations, now can accept operators in identifiers (Rev220)
+- Improved tokenizer for select in optimizations, now can accept operators in identifiers (Rev 220)
 - Uses getopt to handle the command line in a more standard way
 - Organized code so the ui can be either qt or command line
 - Does not depend on QT anymore

relational/optimizations.py

@@ -52,7 +52,17 @@ def replace_node(replace,replacement):
         replace.left=replacement.left
 
 def recoursive_scan(function,node,rels=None):
-    '''Does a recoursive optimization on the tree'''
+    '''Does a recoursive optimization on the tree.
+    
+    This function will recoursively execute the function given
+    as "function" parameter starting from node to all the tree.
+    if rels is provided it will be passed as argument to the function.
+    Otherwise the function will be called just on the node.
+    
+    Result value: function is supposed to return the amount of changes
+    it has performed on the tree.
+    The various result will be added up and this final value will be the
+    returned value.'''
     changes=0
     #recoursive scan
     if node.kind==optimizer.UNARY:
@@ -72,11 +82,20 @@ def recoursive_scan(function,node,rels=None):
 
 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))'''
+    σ a ( σ a(C)) and the ones like σ a ( σ b(C))
+    replacing the 1st one with a single select and
+    the 2nd one with a single select with both conditions
+    in and
+    '''
     changes=0
     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
+            
+            #This adds parenthesis if they are needed
+            if n.child.prop.startswith('(') or n.prop.startswith('('):
+                n.prop= '(%s)' % n.prop
+                
         n.child=n.child.child
         changes=1
         changes+=duplicated_select(n)