引言
SQL注入是一种常见的网络攻击手段，它允许攻击者通过在SQL查询中插入恶意代码，从而非法访问、修改或删除数据库中的数据。UNION查询是SQL中用于合并两个或多个SELECT语句结果集的语句。本文将深入探讨如何巧妙利用UNION查询进行SQL注入攻击，并分析如何防御此类攻击。
UNION查询简介
在正常情况下，UNION查询用于将两个或多个SELECT语句的结果集合并为一个结果集。以下是一个简单的UNION查询示例：
SELECT column_name(s) FROM table1
UNION
SELECT column_name(s) FROM table2;
这个查询会返回table1和table2中所有列的组合，而不考虑重复的行。
利用UNION查询进行SQL注入
攻击者可以通过在UNION查询中插入恶意SQL代码，来绕过数据库的安全防线。以下是一个利用UNION查询进行SQL注入的基本步骤：
发现注入点：攻击者首先需要确定数据库中存在SQL注入漏洞的URL。
构建恶意查询：攻击者构建一个包含UNION语句的恶意查询，尝试从数据库中提取敏感信息。
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