我在过去的几周里学习了PyParsing。我打算用它从SQL语句中获取表名。 我查看了http://pyparsing.wikispaces.com/file/view/simpleSQL.py。但我打算保持简单的语法,因为我不想让每个部分的语句都被解析,而只是寻找表名。此外,还需要为诸如Teradata之类的任何商用现代数据库定义完整的语法。使用pyparsing进行SQL解析
#!/usr/bin/env python
from pyparsing import *
import sys
semicolon = Combine(Literal(';') + lineEnd)
comma = Literal(',')
lparen = Literal('(')
rparen = Literal(')')
# Keyword definition
update_kw, volatile_kw, create_kw, table_kw, as_kw, from_kw, \
where_kw, join_kw, left_kw, right_kw, cross_kw, outer_kw, \
on_kw , insert_kw , into_kw= \
map(lambda x: Keyword(x, caseless=True), \
['UPDATE', 'VOLATILE', 'CREATE', 'TABLE', 'AS', 'FROM',
'WHERE', 'JOIN' , 'LEFT', 'RIGHT' , \
'CROSS', 'OUTER', 'ON', 'INSERT', 'INTO'])
# Teradata SQL allows SELECT and well as SEL keyword
select_kw = Keyword('SELECT', caseless=True) | Keyword('SEL' , caseless=True)
# list of reserved keywords
reserved_words = (update_kw | volatile_kw | create_kw | table_kw | as_kw |
select_kw | from_kw | where_kw | join_kw |
left_kw | right_kw | cross_kw | on_kw | insert_kw |
into_kw)
# Identifier can be used as table or column names. They can't be reserved words
ident = ~reserved_words + Word(alphas, alphanums + '_')
# Recursive definition for table
table = Forward()
# simple table name can be identifer or qualified identifier e.g. schema.table
simple_table = Combine(Optional(ident + Literal('.')) + ident)
# table name can also a complete select statement used as table
nested_table = lparen.suppress() + select_kw.suppress() + SkipTo(from_kw).suppress() + \
from_kw.suppress() + table + rparen.suppress()
# table can be simple table or nested table
table << (nested_table | simple_table)
# comma delimited list of tables
table_list = delimitedList(table)
# Building from clause only because table name(s) will always appears after that
from_clause = from_kw.suppress() + table_list
txt = """
SELECT p, (SELECT * FROM foo),e FROM a, d, (SELECT * FROM z), b
"""
for token, start, end in from_clause.scanString(txt):
print token
这里值得一提的东西。我使用“SkipTo(from_kw)”跳过SQL语句中的列列表。这主要是为了避免为列列表定义语法,可以用逗号分隔列表标识符,许多函数名称,DW分析函数以及不包含的语法。有了这个语法,我可以解析上面的语句以及SELECT列表或列表中的任何级别的嵌套。
['foo']
['a', 'd', 'z', 'b']
我面临的问题时,选择具有where子句:
nested_table = lparen.suppress() + select_kw.suppress() + SkipTo(from_kw).suppress() + \
from_kw.suppress() + table + rparen.suppress()
当WHERE子句是有那么同样的语句可能看起来像: SELECT ... FROM A,d,(SELECT *从z其中(C1 = 1)和(C2 = 3)),p 我想改变 “nested_table” 定义的:
nested_table = lparen.suppress() + select_kw.suppress() + SkipTo(from_kw).suppress() + \
from_kw.suppress() + table + Optional(where_kw + SkipTo(rparen)) + rparen
但是这是行不通的,因为它的权利消减匹配“c = 1”后的合成。我想知道的是如何跳到右括号匹配左括号右“SELECT * FROM z ...”之前我不知道如何使用PyParsing
另外在不同的笔记上我寻求一些建议,从复杂的嵌套SQL获取表名的最佳方式。任何帮助真的很感激。
感谢 作者Abhijit
任何人的帮助? –