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git-svn-id: http://galileo.dmi.unict.it/svn/relational/trunk@187 014f5005-505e-4b48-8d0a-63407b615a7c
This commit is contained in:
LtWorf 2009-06-09 09:05:48 +00:00
parent 7659e39bd3
commit dd43097d7e
1 changed files with 23 additions and 5 deletions
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28
relational/optimizer.py
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@ -48,21 +48,37 @@ class node (object):
return
'''Generates the tree from the tokenized expression'''
while len(expression)==1 and isinstance(expression[0],list): #We have a list, removing
#If the list contains only a list, it will consider the lower level list.
#This will allow things like ((((((a))))) to work
while len(expression)==1 and isinstance(expression[0],list):
expression=expression[0]
if len(expression)==1 and isinstance(expression[0],str): #We have a string (relation name)
#The list contains only 1 string. Means it is the name of a relation
if len(expression)==1 and isinstance(expression[0],str):
self.kind=RELATION
self.name=expression[0]
return
for i in range(len(expression)-1,-1,-1): #Expression from right to left
'''Expression from right to left, searching for binary operators
this means that binary operators have lesser priority than
unary operators.
It find the operator with lesser priority, uses it as root of this
(sub)tree using everything on its left as left parameter (so building
a left subtree with the part of the list located on left) and doing
the same on right.
Since it searches for strings, and expressions into parenthesis are
within sub-lists, they won't be found here, ensuring that they will
have highest priority.'''
for i in range(len(expression)-1,-1,-1):
if expression[i] in b_operators: #Binary operator
self.kind=BINARY
self.name=expression[i]
self.left=node(expression[:i])
self.right=node(expression[i+1:])
return
for i in range(len(expression)-1,-1,-1): #Expression from right to left
'''Searches for unary operators, parsing from right to left'''
for i in range(len(expression)-1,-1,-1):
if expression[i] in u_operators: #Unary operator
self.kind=UNARY
self.name=expression[i]
@ -154,7 +170,7 @@ def tokenize(expression):
sub-expression: this status is entered when finding a '(' and will be exited when finding a ')'.
means that the others open must be counted to determine which close is the right one.'''
expression=expression.strip()
expression=expression.strip() #Removes initial and endind spaces
state=0
'''
0 initial and useless
@ -178,7 +194,9 @@ def tokenize(expression):
if par_count==0:
end=i
break
#Appends the tokenization of the content of the parenthesis
items.append(tokenize(expression[1:end]))
#Removes the entire parentesis and content from the expression
expression=expression[end+1:].strip()
elif expression.startswith("σ") or expression.startswith("π") or expression.startswith("ρ"): #Unary 2 bytes