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[Wie extrahiere ich Spalteninformationen in Datenbankabfrageergebnissen mit MySQLI_Result :: fetch_fields?

gitbox 2025-09-16 
<span><span><span class="hljs-meta">&lt;?php</span></span><span>
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</span><span><span class="hljs-meta">&lt;?php</span></span><span>
<span class="hljs-comment">/*
Titel: verwenden mysqli_result::fetch_fields So extrahieren Sie Spalteninformationen aus Datenbankabfrageergebnissen？
*/</span>

</span><span><span class="hljs-comment">// 在verwenden PHP arbeiten MySQL Wenn die Datenbank，Oft müssen Sie Spalteninformationen in Abfrageergebnissen abrufen，Zum Beispiel Spaltennamen、Datentyp、Länge usw.。mysqli Bereitgestellt fetch_fields Methoden, um diese Informationen leicht zu extrahieren。</span></span><span>

</span><span><span class="hljs-comment">// 1. Stellen Sie eine Verbindung zur Datenbank her</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">$mysqli</span></span><span>-&gt;connect_error) {
    </span><span><span class="hljs-keyword">die</span></span><span>(</span><span><span class="hljs-string">"Verbindung ist fehlgeschlagen: "</span></span><span> . </span><span><span class="hljs-variable">$mysqli</span></span><span>-&gt;connect_error);
}

</span><span><span class="hljs-comment">// 2. Eine Frage ausführen</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">$result</span></span><span>) {
    </span><span><span class="hljs-comment">// 3. verwenden fetch_fields Spalteninformationen extrahieren</span></span><span>
    </span><span><span class="hljs-variable">$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;Abfragenergebnisspalteninformationen：&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">"Listen Sie den Namen auf: "</span></span><span> . </span><span><span class="hljs-variable">$field</span></span><span>-&gt;name . </span><span><span class="hljs-string">"&lt;br&gt;"</span></span><span>;
        </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"Tabellenname: "</span></span><span> . </span><span><span class="hljs-variable">$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">"Datentyp: "</span></span><span> . </span><span><span class="hljs-variable">$field</span></span><span>-&gt;type . </span><span><span class="hljs-string">"&lt;br&gt;"</span></span><span>;
        </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"Länge: "</span></span><span> . </span><span><span class="hljs-variable">$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Länge: "</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. Iterieren Sie über das Ergebnissatz</span></span><span>
    </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"&lt;h2&gt;Abfrageergebnisdaten：&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">$result</span></span><span>-&gt;</span><span><span class="hljs-title function_ invoke__">free</span></span><span>();
} </span><span><span class="hljs-keyword">else</span></span><span> {
    </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"Abfrage fehlgeschlagen: "</span></span><span> . </span><span><span class="hljs-variable">$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">/*
Zusammenfassen：
- mysqli_result::fetch_fields() Kann ein Array mit allen Spalteninformationen zurückgeben。
- Jedes Array -Element ist ein Objekt，包含Listen Sie den Namen auf(name)、Tabellenname(table)、Datentyp(type)、Länge(length)usw.。
- Dies erzeugt dynamisch Tabellen、Sehr nützlich beim Exportieren von Daten oder beim Debuggen von Datenbankstrukturen。
*/</span>
</span><span><span class="hljs-meta">?&gt;</span></span><span>
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