如何检查值是否已存在以避免重复？

CREATE UNIQUE INDEX index_name ON table_name (column_name);

SELECT * FROM table_name WHERE column_name = 'value';

import pymysql

# 连接数据库
conn = pymysql.connect(host='localhost', user='root', password='password', db='test', charset='utf8mb4')

# 创建游标对象
cursor = conn.cursor()

# 执行查询语句
cursor.execute('SELECT * FROM table_name WHERE column_name = %s', ('value',))

# 获取查询结果
result = cursor.fetchone()

# 如果查询结果为空，则插入数据
if result is None:
    cursor.execute('INSERT INTO table_name (column_name) VALUES (%s)', ('value',))
    conn.commit()
else:
    print('值已存在')

# 关闭游标和连接
cursor.close()
conn.close()

hash_table = {}

# 检查值是否已存在
if 'value' in hash_table:
    print('值已存在')
else:
    hash_table['value'] = True