def down_select(syntax_tree, sql, relation2):
if syntax_tree.op == 'SELECT':
condition = syntax_tree.cond
sql = condition.split('&')
relation = []
# 找出关系名
for i in range(len(sql)):
if lookfor(sql[i]) is not None:
relation.append(lookfor(sql[i]))
relation2.append(lookfor2(sql[i]))
syntax_tree = down_select(syntax_tree.lfchild, sql, relation2)
elif syntax_tree.op == 'PROJECTION':
# 跳过投影
syntax_tree.lfchild = down_select(syntax_tree.lfchild, sql, relation2)
elif syntax_tree.op == 'JOIN':
# 有JOIN，将SELECT与关系名下推
first_tree = SyntaxTree()
first_tree.op = 'SELECT'
first_tree.cond = sql[0]
first_tree.lfchild = syntax_tree.lfchild
syntax_tree.lfchild = first_tree
if len(sql) == 1:
return syntax_tree
second_tree = SyntaxTree()
second_tree.op = 'SELECT'
second_tree.cond = sql[1]
second_tree.rchild = syntax_tree.rchild
syntax_tree.rchild = second_tree
return syntax_tree
def parsesql(sql_statement):
sql = sql_statement.split()
tree = SyntaxTree()
index = 0
while True:
if index >= len(sql):
break
elif sql[index] == 'SELECT' or sql[index] == 'PROJECTION':
tree.op = sql[index]
index += 2
condition = ''
# 把[]里的内容全部记录下来
while sql[index] != ']':
condition += sql[index]
condition += ' '
index += 1
index += 1
tree.cond = condition
elif sql[index] == 'JOIN':
# 连接操作创建子树
tree.op = sql[index]
tree.lfchild = SyntaxTree()
tree.lfchild.attr = sql[index - 1]
tree.rchild = SyntaxTree()
tree.rchild.attr = sql[index + 1]
index += 1
elif sql[index] == '(':
# 遇到(再创建一个子树
index += 1
statement = ''
while index < len(sql) and sql[index] != ')':
statement += sql[index]
statement += ' '
index += 1
index += 1
tree.lfchild = parsesql(statement) # 递归构造子树
else:
index += 1
return tree
def down_proj(syntax_tree, sql, relation2, same):
if syntax_tree.op == 'SELECT':
syntax_tree.lfchild = down_proj(syntax_tree.lfchild, sql, relation2,
same)
elif syntax_tree.op == 'PROJECTION':
# 将投影下推
sql = syntax_tree.cond.split(",")
for i in range(len(sql)):
if lookfor(sql[i]) is not None:
if lookfor2(sql[i]) in relation2:
pass
else:
relation2.append(lookfor2(sql[i]))
# 找相交的元素
same += findthesame(relation2[0], relation2[1])
syntax_tree.lfchild = down_proj(syntax_tree.lfchild, sql, relation2,
same)
elif syntax_tree.op == 'JOIN':
# 有JOIN，将条件和投影下推
if len(sql) > 0 and '=' not in sql[0]:
first_tree = SyntaxTree()
first_tree.op = 'PROJECTION'
first_tree.cond = sql[0] + ', ' + same
first_tree.lfchild = syntax_tree.lfchild
syntax_tree.lfchild = first_tree
if len(sql) > 1:
second_tree = SyntaxTree()
second_tree.op = 'PROJECTION'
second_tree.cond = sql[1] + ', ' + same
second_tree.rchild = syntax_tree.rchild
syntax_tree.rchild = second_tree
elif same != '':
second_tree = SyntaxTree()
second_tree.op = 'PROJECTION'
second_tree.cond = same
second_tree.rchild = syntax_tree.rchild
syntax_tree.rchild = second_tree
return syntax_tree