因此，我尝试优化给定的SQL查询，如下所示：

SELECT EMPLOYEE.EMPNO, POSITION
FROM EMPLOYEE E, JOBHISTORY J
WHERE E. EMPNO = J. EMPNO
AND STARTDATE <= ENDDATE
AND SALARY <= 3000;

在这里，我想删除开始日期和结束日期，以便用户只需按如下所示键入，然后即可获得结果：

SELECT EMPLOYEE.EMPNO, POSITION
    FROM EMPLOYEE E, JOBHISTORY J
    WHERE E. EMPNO = J. EMPNO
    AND SALARY <= 3000;

我最初开始用Python编写自己的解析器，但真的被难住了，决定四处看看，找出了“sqlparse”库，在库中他们有函数get_names（）是令牌函数的一部分，但是在我的代码中实现它时，我一直收到错误AttributeError 'Token'对象没有属性'get_name'，所以我不确定我做错了什么。下面是我的Python代码：

import sqlparse
import networkx as nx
import matplotlib.pyplot as plt

# example query
query = "SELECT EMPLOYEE.EMPNO, POSITION FROM EMPLOYEE E, JOBHISTORY J WHERE E.EMPNO = J.EMPNO AND STARTDATE <= ENDDATE AND SALARY <= 3000"

# parse the query
parsed_query = sqlparse.parse(query)[0]
select_stmt = parsed_query.tokens[0]

# extract the tables and conditions from the query
tables = []
conditions = []
for token in parsed_query.tokens:
    if isinstance(token, sqlparse.sql.IdentifierList):
        for T in token.get_identifiers():
            tables.append(T.get_name())
    elif isinstance(token, sqlparse.sql.Where):
        for condition in token.tokens:
            if isinstance(condition, sqlparse.sql.Comparison):
                conditions.append(condition)

# remove unnecessary conditions
new_conditions = []
for condition in conditions:
    if "startdate" not in condition.normalized:
        new_conditions.append(condition)
conditions = new_conditions

# generate query tree
G = nx.Graph()
for table in tables:
    G.add_node(table)
for condition in conditions:
    table1 = condition.left.get_name()
    table2 = condition.right.get_name()
    G.add_edge(table1, table2)

# visualize query tree
nx.draw(G, with_labels=True)
plt.show()

# generate optimized query
new_query = select_stmt.to_unicode()
new_query += " FROM " + ", ".join(tables)
new_query += " WHERE " + " AND ".join([str(condition) for condition in conditions])
print(new_query)