PDOStatement::fetchColumn 和 PDOStatement::fetchAll 性能差异有多大？

<span><span><span class="hljs-meta"><?php</span></span><span>
</span><span><span class="hljs-comment">// 下面是与文章内容无关的 PHP 代码示例</span></span><span>
</span><span><span class="hljs-function"><span class="hljs-keyword">function</span></span></span><span> </span><span><span class="hljs-title">randomGreeting</span></span><span>(</span><span><span class="hljs-params"></span></span><span>) {
    </span><span><span class="hljs-variable">$greetings</span></span><span> = [</span><span><span class="hljs-string">"Hello!"</span></span><span>, </span><span><span class="hljs-string">"Hi!"</span></span><span>, </span><span><span class="hljs-string">"Hey there!"</span></span><span>, </span><span><span class="hljs-string">"Greetings!"</span></span><span>];
    </span><span><span class="hljs-keyword">return</span></span><span> </span><span><span class="hljs-variable">$greetings</span></span><span>[</span><span><span class="hljs-title function_ invoke__">array_rand</span></span><span>(</span><span><span class="hljs-variable">$greetings</span></span><span>)];
}

</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-title function_ invoke__">randomGreeting</span></span><span>();
</span><span><span class="hljs-meta">?></span></span><span>

<hr>

</span><span><span class="hljs-meta"><?php</span></span><span>
</span><span><span class="hljs-comment">// 正文内容开始</span></span><span>
</span><span><span class="hljs-meta">?></span></span><span>

<h1></span><span><span class="hljs-title class_">PDOStatement</span></span><span>::</span><span><span class="hljs-variable constant_">fetchColumn</span></span><span> 和 </span><span><span class="hljs-title class_">PDOStatement</span></span><span>::</span><span><span class="hljs-variable constant_">fetchAll</span></span><span> 性能差异有多大？</h1>

<p>在 PHP 中使用 PDO 进行数据库操作时，常常会遇到 <code></span><span><span class="hljs-title class_">PDOStatement</span></span><span>::</span><span><span class="hljs-variable constant_">fetchColumn</span></span><span>

上例中，每次循环只获取一行的 id，内存消耗极低。

fetchAll 示例：

</span><span><span class="hljs-variable">$stmt</span></span><span> = </span><span><span class="hljs-variable">$pdo</span></span><span>-></span><span><span class="hljs-title function_ invoke__">query</span></span><span>(</span><span><span class="hljs-string">"SELECT id, name FROM users"</span></span><span>);
</span><span><span class="hljs-variable">$rows</span></span><span> = </span><span><span class="hljs-variable">$stmt</span></span><span>-></span><span><span class="hljs-title function_ invoke__">fetchAll</span></span><span>(PDO::</span><span><span class="hljs-variable constant_">FETCH_ASSOC</span></span><span>);
</span><span><span class="hljs-keyword">foreach</span></span><span> (</span><span><span class="hljs-variable">$rows</span></span><span> </span><span><span class="hljs-keyword">as</span></span><span> </span><span><span class="hljs-variable">$row</span></span><span>) {
    </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-variable">$row</span></span><span>[</span><span><span class="hljs-string">'id'</span></span><span>] . </span><span><span class="hljs-string">' - '</span></span><span> . </span><span><span class="hljs-variable">$row</span></span><span>[</span><span><span class="hljs-string">'name'</span></span><span>] . </span><span><span class="hljs-string">"\n"</span></span><span>;
}

fetchAll 会一次性将整个结果集加载到内存，如果表非常大，可能会影响性能。

4. 总结

综上所述：

• 如果只需要单列或少量数据，fetchColumn() 是首选，更节省内存且性能更好。
• 如果需要一次性处理整个结果集并且数据量可控，fetchAll() 更方便，但对内存要求更高。
• 在大数据量场景下，尽量避免 fetchAll，改用 fetch 或 fetchColumn 分批处理。