python - 在 Python 中根据函数名拆分 SQL 语句但保留分隔符

Question

假设我有以下字符串，其中包含从SELECT子句中提取的SQL语句(实际上，这是一个包含数百条此类语句的巨大SQL语句)；

  SUM(case when(A.money-B.money>1000
                and A.unixtime-B.unixtime<=890769
                and B.col10 = "A"
                and B.col11 = "12"
                and B.col12 = "V") then 10
      end) as finalCond0,
  MAX(case when(A.money-B.money<0
                and A.unixtime-B.unixtime<=6786000
                and B.cond1 = "A"
                and B.cond2 = "4321"
                and B.cond3 in ("E", "F", "G")) then A.col10
        end) as finalCond1,
  SUM(case when(A.money-B.money>0
                and A.unixtime-B.unixtime<=6786000
                and B.cond1 = "A"
                and B.cond2 = "1234"
                and B.cond3 in ("A", "B", "C")) then 2
      end) as finalCond2    

如何在函数上拆分此查询(即 SUM、MAX、MIN、MEAN 等。 )这样我就可以提取最后一个查询，但不删除分隔符(在本例中为 SUM)？

因此所需的输出将是如下所示的字符串:

  SUM(case when(A.money-B.money>0
                and A.unixtime-B.unixtime<=6786000
                and B.cond1 = "A"
                and B.cond2 = "1234"
                and B.cond3 in ("A", "B", "C")) then 2
      end) as finalCond2

PS:出于演示目的，我提供了某种缩进，但实际上这些语句是用逗号分隔的，这意味着原始形式中不会出现空格或换行符。

Answer 1

这里不能使用正则表达式，因为 SQL 语法不形成可以与 Python re 引擎匹配的正则模式。您必须将字符串实际解析为 token 流或语法树；毕竟，您的 SUM(...) 可以包含多种语法，包括子选择。

sqlparse library可以做到这一点，即使它是 bit underdocumented and not that friendly to external uses .

重新使用我在链接到的另一篇文章中定义的 walk_tokens 函数:

from collections import deque
from sqlparse.sql import TokenList

def walk_tokens(token):
    queue = deque([token])
    while queue:
        token = queue.popleft()
        if isinstance(token, TokenList):
            queue.extend(token)
        yield token

从 SELECT 标识符列表中提取最后一个元素是:

import sqlparse
from sqlparse.sql import IdentifierList

tokens = sqlparse.parse(sql)[0]
for tok in walk_tokens(tokens):
    if isinstance(tok, IdentifierList):
        # iterate to leave the last assigned to `identifier`
        for identifier in tok.get_identifiers():
            pass
        break

print(identifier)

演示:

>>> sql = '''\
...   SUM(case when(A.money-B.money>1000
...                 and A.unixtime-B.unixtime<=890769
...                 and B.col10 = "A"
...                 and B.col11 = "12"
...                 and B.col12 = "V") then 10
...       end) as finalCond0,
...   MAX(case when(A.money-B.money<0
...                 and A.unixtime-B.unixtime<=6786000
...                 and B.cond1 = "A"
...                 and B.cond2 = "4321"
...                 and B.cond3 in ("E", "F", "G")) then A.col10
...         end) as finalCond1,
...   SUM(case when(A.money-B.money>0
...                 and A.unixtime-B.unixtime<=6786000
...                 and B.cond1 = "A"
...                 and B.cond2 = "1234"
...                 and B.cond3 in ("A", "B", "C")) then 2
...       end) as finalCond2
... '''
>>> tokens = sqlparse.parse(sql)[0]
>>> for tok in walk_tokens(tokens):
...     if isinstance(tok, IdentifierList):
...         # iterate to leave the last assigned to `identifier`
...         for identifier in tok.get_identifiers():
...             pass
...         break
...
>>> print(identifier)
SUM(case when(A.money-B.money>0
                and A.unixtime-B.unixtime<=6786000
                and B.cond1 = "A"
                and B.cond2 = "1234"
                and B.cond3 in ("A", "B", "C")) then 2
      end) as finalCond2

identifier 是一个 sqlparse.sql.Identifier 实例，但再次将其转换为字符串(print() 会这样做，或者您只需使用 str()) 即可再次为您提供该部分的输入 SQL 字符串。