[使用 mysqli_result::fetch_fields 如何提取数据库查询结果中的列信息？

gitbox 2025-09-16
<span><span><span class="hljs-meta">&lt;?php</span></span><span>
</span><span><span class="hljs-comment">// 与文章内容无关的PHP代码示例</span></span><span>
</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"欢迎来到我的PHP教程页面！"</span></span><span>;
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</span><span><span class="hljs-meta">&lt;?php</span></span><span>
<span class="hljs-comment">/*
标题: 使用 mysqli_result::fetch_fields 如何提取数据库查询结果中的列信息？
*/</span>

</span><span><span class="hljs-comment">// 在使用 PHP 操作 MySQL 数据库时，经常需要获取查询结果中的列信息，例如列名、数据类型、长度等。mysqli 提供了 fetch_fields 方法来方便地提取这些信息。</span></span><span>

</span><span><span class="hljs-comment">// 1. 连接数据库</span></span><span>
</span><span><span class="hljs-variable">$servername</span></span><span> = </span><span><span class="hljs-string">"localhost"</span></span><span>;
</span><span><span class="hljs-variable">$username</span></span><span> = </span><span><span class="hljs-string">"root"</span></span><span>;
</span><span><span class="hljs-variable">$password</span></span><span> = </span><span><span class="hljs-string">""</span></span><span>;
</span><span><span class="hljs-variable">$database</span></span><span> = </span><span><span class="hljs-string">"test_db"</span></span><span>;

</span><span><span class="hljs-variable">$mysqli</span></span><span> = </span><span><span class="hljs-keyword">new</span></span><span> </span><span><span class="hljs-title function_ invoke__">mysqli</span></span><span>(</span><span><span class="hljs-variable">$servername</span></span><span>, </span><span><span class="hljs-variable">$username</span></span><span>, </span><span><span class="hljs-variable">$password</span></span><span>, </span><span><span class="hljs-variable">$database</span></span><span>);

</span><span><span class="hljs-keyword">if</span></span><span> (</span><span><span class="hljs-variable">$mysqli</span></span><span>-&gt;connect_error) {
    </span><span><span class="hljs-keyword">die</span></span><span>(</span><span><span class="hljs-string">"连接失败: "</span></span><span> . </span><span><span class="hljs-variable">$mysqli</span></span><span>-&gt;connect_error);
}

</span><span><span class="hljs-comment">// 2. 执行查询</span></span><span>
</span><span><span class="hljs-variable">$sql</span></span><span> = </span><span><span class="hljs-string">"SELECT id, name, email FROM users"</span></span><span>;
</span><span><span class="hljs-variable">$result</span></span><span> = </span><span><span class="hljs-variable">$mysqli</span></span><span>-&gt;</span><span><span class="hljs-title function_ invoke__">query</span></span><span>(</span><span><span class="hljs-variable">$sql</span></span><span>);

</span><span><span class="hljs-keyword">if</span></span><span> (</span><span><span class="hljs-variable">$result</span></span><span>) {
    </span><span><span class="hljs-comment">// 3. 使用 fetch_fields 提取列信息</span></span><span>
    </span><span><span class="hljs-variable">$fields</span></span><span> = </span><span><span class="hljs-variable">$result</span></span><span>-&gt;</span><span><span class="hljs-title function_ invoke__">fetch_fields</span></span><span>();

    </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"&lt;h2&gt;查询结果列信息：&lt;/h2&gt;"</span></span><span>;
    </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"&lt;ul&gt;"</span></span><span>;
    </span><span><span class="hljs-keyword">foreach</span></span><span> (</span><span><span class="hljs-variable">$fields</span></span><span> </span><span><span class="hljs-keyword">as</span></span><span> </span><span><span class="hljs-variable">$field</span></span><span>) {
        </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"&lt;li&gt;"</span></span><span>;
        </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"列名: "</span></span><span> . </span><span><span class="hljs-variable">$field</span></span><span>-&gt;name . </span><span><span class="hljs-string">"&lt;br&gt;"</span></span><span>;
        </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"表名: "</span></span><span> . </span><span><span class="hljs-variable">$field</span></span><span>-&gt;table . </span><span><span class="hljs-string">"&lt;br&gt;"</span></span><span>;
        </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"数据类型: "</span></span><span> . </span><span><span class="hljs-variable">$field</span></span><span>-&gt;type . </span><span><span class="hljs-string">"&lt;br&gt;"</span></span><span>;
        </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"长度: "</span></span><span> . </span><span><span class="hljs-variable">$field</span></span><span>-&gt;length . </span><span><span class="hljs-string">"&lt;br&gt;"</span></span><span>;
        </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"最大长度: "</span></span><span> . </span><span><span class="hljs-variable">$field</span></span><span>-&gt;max_length . </span><span><span class="hljs-string">"&lt;br&gt;"</span></span><span>;
        </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"&lt;/li&gt;&lt;br&gt;"</span></span><span>;
    }
    </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"&lt;/ul&gt;"</span></span><span>;

    </span><span><span class="hljs-comment">// 4. 遍历结果集</span></span><span>
    </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"&lt;h2&gt;查询结果数据：&lt;/h2&gt;"</span></span><span>;
    </span><span><span class="hljs-keyword">while</span></span><span> (</span><span><span class="hljs-variable">$row</span></span><span> = </span><span><span class="hljs-variable">$result</span></span><span>-&gt;</span><span><span class="hljs-title function_ invoke__">fetch_assoc</span></span><span>()) {
        </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"ID: "</span></span><span> . </span><span><span class="hljs-variable">$row</span></span><span>[</span><span><span class="hljs-string">'id'</span></span><span>] . </span><span><span class="hljs-string">", Name: "</span></span><span> . </span><span><span class="hljs-variable">$row</span></span><span>[</span><span><span class="hljs-string">'name'</span></span><span>] . </span><span><span class="hljs-string">", Email: "</span></span><span> . </span><span><span class="hljs-variable">$row</span></span><span>[</span><span><span class="hljs-string">'email'</span></span><span>] . </span><span><span class="hljs-string">"&lt;br&gt;"</span></span><span>;
    }

    </span><span><span class="hljs-variable">$result</span></span><span>-&gt;</span><span><span class="hljs-title function_ invoke__">free</span></span><span>();
} </span><span><span class="hljs-keyword">else</span></span><span> {
    </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"查询失败: "</span></span><span> . </span><span><span class="hljs-variable">$mysqli</span></span><span>-&gt;error;
}

</span><span><span class="hljs-variable">$mysqli</span></span><span>-&gt;</span><span><span class="hljs-title function_ invoke__">close</span></span><span>();

<span class="hljs-comment">/*
总结：
- mysqli_result::fetch_fields() 可以返回一个包含所有列信息的数组。
- 每个数组元素是一个对象，包含列名(name)、表名(table)、数据类型(type)、长度(length)等属性。
- 这在动态生成表格、数据导出或调试数据库结构时非常有用。
*/</span>
</span><span><span class="hljs-meta">?&gt;</span></span><span>
</span></span>
相关标签:
mysqli_result
mysqli_result::fetch_fields