def union_and_product(n):
'''
A * B ∪ A * C = A * (B ∪ C)
Same thing with inner join
'''
changes = 0
if n.name == UNION and n.left.name in {PRODUCT, JOIN} and n.left.name == n.right.name:
newnode = parser.node()
newnode.kind = parser.BINARY
newnode.name = n.left.name
newchild = parser.node()
newchild.kind = parser.BINARY
newchild.name = UNION
if n.left.left == n.right.left or n.left.left == n.right.right:
newnode.left = n.left.left
newnode.right = newchild
newchild.left = n.left.right
newchild.right = n.right.left if n.left.left == n.right.right else n.right.right
replace_node(n, newnode)
changes = 1
elif n.left.right == n.right.left or n.left.left == n.right.right:
newnode.left = n.left.right
newnode.right = newchild
newchild.left = n.left.left
newchild.right = n.right.left if n.right.left == n.right.right else n.right.right
replace_node(n, newnode)
changes = 1
return changes + recoursive_scan(union_and_product, n)
def down_to_unions_subtractions_intersections(n):
'''This funcion locates things like σ i==2 (c ᑌ d), where the union
can be a subtraction and an intersection and replaces them with
σ i==2 (c) ᑌ σ i==2(d).
'''
changes = 0
_o = (UNION, DIFFERENCE, INTERSECTION)
if n.name == SELECTION and n.child.name in _o:
left = parser.node()
left.prop = n.prop
left.name = n.name
left.child = n.child.left
left.kind = parser.UNARY
right = parser.node()
right.prop = n.prop
right.name = n.name
right.child = n.child.right
right.kind = parser.UNARY
n.name = n.child.name
n.left = left
n.right = right
n.child = None
n.prop = None
n.kind = parser.BINARY
changes += 1
return changes + recoursive_scan(down_to_unions_subtractions_intersections, 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 O(n²) operation like the union'''
changes = 0
if n.name in (UNION, INTERSECTION, DIFFERENCE) and n.left.name == SELECTION and n.right.name == SELECTION and n.left.child == n.right.child:
cahnges = 1
d = {UNION: 'or', INTERSECTION: 'and', DIFFERENCE: 'and not'}
op = d[n.name]
newnode = parser.node()
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
replace_node(n, newnode)
return changes + recoursive_scan(select_union_intersect_subtract, 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 O(n²) operation like the union'''
changes = 0
if n.name in {UNION, INTERSECTION, DIFFERENCE} and \
n.left.name == SELECTION and \
n.right.name == SELECTION and \
n.left.child == n.right.child:
changes = 1
d = {UNION: 'or', INTERSECTION: 'and', DIFFERENCE: 'and not'}
op = d[n.name]
newnode = parser.node()
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
replace_node(n, newnode)
return changes + recoursive_scan(select_union_intersect_subtract, n)
def swap_union_renames(n):
'''This function locates things like
ρ a➡b(R) ᑌ ρ a➡b(Q)
and replaces them with
ρ a➡b(R ᑌ Q).
Does the same with subtraction and intersection'''
changes = 0
if n.name in (DIFFERENCE, UNION, INTERSECTION) and n.left.name == n.right.name and n.left.name == RENAME:
l_vars = {}
for i in n.left.prop.split(','):
q = i.split(ARROW)
l_vars[q[0].strip()] = q[1].strip()
r_vars = {}
for i in n.right.prop.split(','):
q = i.split(ARROW)
r_vars[q[0].strip()] = q[1].strip()
if r_vars == l_vars:
changes = 1
# Copying self, but child will be child of renames
q = parser.node()
q.name = n.name
q.kind = parser.BINARY
q.left = n.left.child
q.right = n.right.child
n.name = RENAME
n.kind = parser.UNARY
n.child = q
n.prop = n.left.prop
n.left = n.right = None
return changes + recoursive_scan(swap_union_renames, 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,
i contains attributes belonging to Q and l contains attributes belonging to both'''
changes = 0
if n.name == SELECTION and n.child.name in (PRODUCT, JOIN):
l_attr = n.child.left.result_format(rels)
r_attr = n.child.right.result_format(rels)
tokens = tokenize_select(n.prop)
groups = []
temp = []
for i in tokens:
if i == 'and' and i.level == 0:
groups.append(temp)
temp = []
else:
temp.append(i)
if len(temp) != 0:
groups.append(temp)
temp = []
left = []
right = []
both = []
for i in groups:
l_fields = False # has fields in left?
r_fields = False # has fields in left?
for j in set(i).difference(sel_op):
j = j.split('.')[0]
if j in l_attr: # Field in left
l_fields = True
if j in r_attr: # Field in right
r_fields = True
if l_fields and r_fields: # Fields in both
both.append(i)
elif l_fields:
left.append(i)
elif r_fields:
right.append(i)
else: # Unknown.. adding in both
both.append(i)
# Preparing left selection
if len(left) > 0:
changes = 1
l_node = parser.node()
l_node.name = SELECTION
l_node.kind = parser.UNARY
l_node.child = n.child.left
l_node.prop = ''
n.child.left = l_node
while len(left) > 0:
c = left.pop(0)
for i in c:
l_node.prop += i + ' '
if len(left) > 0:
l_node.prop += ' and '
if '(' in l_node.prop:
l_node.prop = '(%s)' % l_node.prop
# Preparing right selection
if len(right) > 0:
changes = 1
r_node = parser.node()
r_node.name = SELECTION
r_node.prop = ''
r_node.kind = parser.UNARY
r_node.child = n.child.right
n.child.right = r_node
while len(right) > 0:
c = right.pop(0)
r_node.prop += ' '.join(c)
if len(right) > 0:
r_node.prop += ' and '
if '(' in r_node.prop:
r_node.prop = '(%s)' % r_node.prop
# Changing main selection
n.prop = ''
if len(both) != 0:
while len(both) > 0:
c = both.pop(0)
n.prop += ' '.join(c)
if len(both) > 0:
n.prop += ' and '
if '(' in n.prop:
n.prop = '(%s)' % n.prop
else: # No need for general select
replace_node(n, n.child)
return changes + recoursive_scan(selection_and_product, n, rels)