如何从SQL查询中提取表名和列名? [英] How to extract table names and column names from sql query?

问题描述

所以假设我们有这样简单的查询:

So let assume we have such simple query:

Select a.col1, b.col2 from tb1 as a inner join tb2 as b on tb1.col7 = tb2.col8;

结果应如下所示:

tb1 col1
tb1 col7
tb2 col2
tb2 col8

我尝试使用一些python库解决此问题:

I've tried to solve this problem using some python library:

1)即使仅使用sqlparse提取表也可能是一个巨大的问题.例如，这官方书籍根本无法正常工作

1) Even extracting only tables using sqlparse might be a huge problem. For example this official book doesn't work properly at all.

2)使用正则表达式似乎很难实现.

2) Using regular expression seems to be really hard to achieve.

3)但后来我发现这，可能会有所帮助.但是问题是我无法连接到任何数据库并执行该查询.

3) But then I found this , that might help. However the problem is that I can't connect to any database and execute that query.

有什么想法吗?

推荐答案

真的，这不是一件容易的事.您可以使用词法分析器(在此示例中为 ply )并定义一些规则以从细绳.以下代码为SQL字符串的不同部分定义了这些规则，并将它们放回一起，因为输入字符串中可能会有别名.如此一来，您将获得一个字典(result)，它具有不同的表名作为键.

Really, this is no easy task. You could use a lexer (ply in this example) and define several rules to get several tokens out of a string. The following code defines these rules for the different parts of your SQL string and puts them back together as there could be aliases in the input string. As a result, you get a dictionary (result) with the different tablenames as key.

import ply.lex as lex, re

tokens = (
    "TABLE",
    "JOIN",
    "COLUMN",
    "TRASH"
)

tables = {"tables": {}, "alias": {}}
columns = []

t_TRASH = r"Select|on|=|;|\s+|,|\t|\r"

def t_TABLE(t):
    r"from\s(\w+)\sas\s(\w+)"

    regex = re.compile(t_TABLE.__doc__)
    m = regex.search(t.value)
    if m is not None:
        tbl = m.group(1)
        alias = m.group(2)
        tables["tables"][tbl] = ""
        tables["alias"][alias] = tbl

    return t

def t_JOIN(t):
    r"inner\s+join\s+(\w+)\s+as\s+(\w+)"

    regex = re.compile(t_JOIN.__doc__)
    m = regex.search(t.value)
    if m is not None:
        tbl = m.group(1)
        alias = m.group(2)
        tables["tables"][tbl] = ""
        tables["alias"][alias] = tbl
    return t

def t_COLUMN(t):
    r"(\w+\.\w+)"

    regex = re.compile(t_COLUMN.__doc__)
    m = regex.search(t.value)
    if m is not None:
        t.value = m.group(1)
        columns.append(t.value)
    return t

def t_error(t):
    raise TypeError("Unknown text '%s'" % (t.value,))
    t.lexer.skip(len(t.value))

# here is where the magic starts
def mylex(inp):
    lexer = lex.lex()
    lexer.input(inp)

    for token in lexer:
        pass

    result = {}
    for col in columns:
        tbl, c = col.split('.')
        if tbl in tables["alias"].keys():
            key = tables["alias"][tbl]
        else:
            key = tbl

        if key in result:
            result[key].append(c)
        else:
            result[key] = list()
            result[key].append(c)

    print result
    # {'tb1': ['col1', 'col7'], 'tb2': ['col2', 'col8']}    

string = "Select a.col1, b.col2 from tb1 as a inner join tb2 as b on tb1.col7 = tb2.col8;"
mylex(string)

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