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python - 在函数名称上拆分 SQL 语句，但在 Python 中保留分隔符

问题描述

假设我有以下string包含从SELECT子句中提取的 SQL 语句（实际上这是一个包含数百个此类语句的巨大 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（即SUM, MAX,等）上拆分此查询，以便我可以提取最后一个查询但不删除分隔符（在本例中为MIN）？MEANSUM

因此，所需的输出将是一个字符串，如下所示：

  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，但实际上这些语句用逗号分隔，这意味着原始形式中不会出现空格或换行符。

标签： pythonsqlregexsplit

解决方案

您不能在此处使用正则表达式，因为 SQL 语法不会形成您可以与 Pythonre引擎匹配的正则模式。您必须将字符串实际解析为令牌流或语法树；SUM(...)毕竟，您可以包含多种语法，包括子选择。

该sqlparse库可以做到这一点，即使它有点缺乏文档并且对外部使用不那么友好。

重新使用walk_tokens我在链接到的另一篇文章中定义的函数：

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

SELECT从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，但是再次将其转换为字符串（print()确实如此，或者您可以使用str()）再次为您提供该部分的输入 SQL 字符串。

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