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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html> <head> <title>Selects the default database for database queries</title> <meta http-equiv="content-type" content="text/html; charset=UTF-8"> </head> <body><div style="text-align: center;"> <div class="prev" style="text-align: left; float: left;"><a href="mysqli.rollback.html">mysqli::rollback</a></div> <div class="next" style="text-align: right; float: right;"><a href="mysqli.set-charset.html">mysqli::set_charset</a></div> <div class="up"><a href="class.mysqli.html">MySQLi</a></div> <div class="home"><a href="index.html">PHP Manual</a></div></div><hr /><div id="mysqli.select-db" class="refentry"> <div class="refnamediv"> <h1 class="refname">mysqli::select_db</h1> <h1 class="refname">mysqli_select_db</h1> <p class="verinfo">(PHP 5)</p><p class="refpurpose"><span class="refname">mysqli::select_db</span> -- <span class="refname">mysqli_select_db</span> — <span class="dc-title">Selects the default database for database queries</span></p> </div> <div class="refsect1 description"> <h3 class="title">Description</h3> <p class="para">Object oriented style (method):</p> <div class="methodsynopsis dc-description"> <span class="type">bool</span> <span class="methodname"><b><b>mysqli::select_db</b></b></span> ( <span class="methodparam"><span class="type">string</span> <tt class="parameter">$dbname</tt></span> )</div> <p class="para rdfs-comment">Procedural style:</p> <div class="methodsynopsis dc-description"> <span class="type">bool</span> <span class="methodname"><b><b>mysqli_select_db</b></b></span> ( <span class="methodparam"><span class="type"><a href="class.mysqli.html" class="type mysqli">mysqli</a></span> <tt class="parameter">$link</tt></span> , <span class="methodparam"><span class="type">string</span> <tt class="parameter">$dbname</tt></span> )</div> <p class="para rdfs-comment"> Selects the default database to be used when performing queries against the database connection. </p> <blockquote><p><b class="note">Note</b>: This function should only be used to change the default database for the connection. You can select the default database with 4th parameter in <a href="mysqli.connect.html" class="function">mysqli_connect()</a>. <br /> </p></blockquote> </div> <div class="refsect1 parameters"> <h3 class="title">Parameters</h3> <p class="para"> <dl> <dt><span class="term"><i><tt class="parameter">link</tt></i></span><dd><p class="para">Procedural style only: A link identifierreturned by <a href="mysqli.connect.html" class="function">mysqli_connect()</a> or <a href="mysqli.init.html" class="function">mysqli_init()</a></p></dd></dt> <dt> <span class="term"><i><tt class="parameter">dbname</tt></i></span> <dd> <p class="para"> The database name. </p> </dd> </dt> </dl> </p> </div> <div class="refsect1 returnvalues"> <h3 class="title">Return Values</h3> <p class="para"> Returns <b><tt>TRUE</tt></b> on success or <b><tt>FALSE</tt></b> on failure. </p> </div> <div class="refsect1 examples"> <h3 class="title">Examples</h3> <div class="example"> <p><b>Example #1 Object oriented style</b></p> <div class="example-contents"><div class="phpcode"><code><span style="color: #000000"><span style="color: #0000BB"><?php<br />$mysqli </span><span style="color: #007700">= new </span><span style="color: #0000BB">mysqli</span><span style="color: #007700">(</span><span style="color: #DD0000">"localhost"</span><span style="color: #007700">, </span><span style="color: #DD0000">"my_user"</span><span style="color: #007700">, </span><span style="color: #DD0000">"my_password"</span><span style="color: #007700">, </span><span style="color: #DD0000">"test"</span><span style="color: #007700">);<br /><br /></span><span style="color: #FF8000">/* check connection */<br /></span><span style="color: #007700">if (</span><span style="color: #0000BB">mysqli_connect_errno</span><span style="color: #007700">()) {<br /> </span><span style="color: #0000BB">printf</span><span style="color: #007700">(</span><span style="color: #DD0000">"Connect failed: %s\n"</span><span style="color: #007700">, </span><span style="color: #0000BB">mysqli_connect_error</span><span style="color: #007700">());<br /> exit();<br />}<br /><br /></span><span style="color: #FF8000">/* return name of current default database */<br /></span><span style="color: #007700">if (</span><span style="color: #0000BB">$result </span><span style="color: #007700">= </span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-></span><span style="color: #0000BB">query</span><span style="color: #007700">(</span><span style="color: #DD0000">"SELECT DATABASE()"</span><span style="color: #007700">)) {<br /> </span><span style="color: #0000BB">$row </span><span style="color: #007700">= </span><span style="color: #0000BB">$result</span><span style="color: #007700">-></span><span style="color: #0000BB">fetch_row</span><span style="color: #007700">();<br /> </span><span style="color: #0000BB">printf</span><span style="color: #007700">(</span><span style="color: #DD0000">"Default database is %s.\n"</span><span style="color: #007700">, </span><span style="color: #0000BB">$row</span><span style="color: #007700">[</span><span style="color: #0000BB">0</span><span style="color: #007700">]);<br /> </span><span style="color: #0000BB">$result</span><span style="color: #007700">-></span><span style="color: #0000BB">close</span><span style="color: #007700">();<br />}<br /><br /></span><span style="color: #FF8000">/* change db to world db */<br /></span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-></span><span style="color: #0000BB">select_db</span><span style="color: #007700">(</span><span style="color: #DD0000">"world"</span><span style="color: #007700">);<br /><br /></span><span style="color: #FF8000">/* return name of current default database */<br /></span><span style="color: #007700">if (</span><span style="color: #0000BB">$result </span><span style="color: #007700">= </span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-></span><span style="color: #0000BB">query</span><span style="color: #007700">(</span><span style="color: #DD0000">"SELECT DATABASE()"</span><span style="color: #007700">)) {<br /> </span><span style="color: #0000BB">$row </span><span style="color: #007700">= </span><span style="color: #0000BB">$result</span><span style="color: #007700">-></span><span style="color: #0000BB">fetch_row</span><span style="color: #007700">();<br /> </span><span style="color: #0000BB">printf</span><span style="color: #007700">(</span><span style="color: #DD0000">"Default database is %s.\n"</span><span style="color: #007700">, </span><span style="color: #0000BB">$row</span><span style="color: #007700">[</span><span style="color: #0000BB">0</span><span style="color: #007700">]);<br /> </span><span style="color: #0000BB">$result</span><span style="color: #007700">-></span><span style="color: #0000BB">close</span><span style="color: #007700">();<br />}<br /><br /></span><span style="color: #0000BB">$mysqli</span><span style="color: #007700">-></span><span style="color: #0000BB">close</span><span style="color: #007700">();<br /></span><span style="color: #0000BB">?></span></span></code></div> </div> </div> <div class="example"> <p><b>Example #2 Procedural style</b></p> <div class="example-contents"><div class="phpcode"><code><span style="color: #000000"><span style="color: #0000BB"><?php<br />$link </span><span style="color: #007700">= </span><span style="color: #0000BB">mysqli_connect</span><span style="color: #007700">(</span><span style="color: #DD0000">"localhost"</span><span style="color: #007700">, </span><span style="color: #DD0000">"my_user"</span><span style="color: #007700">, </span><span style="color: #DD0000">"my_password"</span><span style="color: #007700">, </span><span style="color: #DD0000">"test"</span><span style="color: #007700">);<br /><br /></span><span style="color: #FF8000">/* check connection */<br /></span><span style="color: #007700">if (</span><span style="color: #0000BB">mysqli_connect_errno</span><span style="color: #007700">()) {<br /> </span><span style="color: #0000BB">printf</span><span style="color: #007700">(</span><span style="color: #DD0000">"Connect failed: %s\n"</span><span style="color: #007700">, </span><span style="color: #0000BB">mysqli_connect_error</span><span style="color: #007700">());<br /> exit();<br />}<br /><br /></span><span style="color: #FF8000">/* return name of current default database */<br /></span><span style="color: #007700">if (</span><span style="color: #0000BB">$result </span><span style="color: #007700">= </span><span style="color: #0000BB">mysqli_query</span><span style="color: #007700">(</span><span style="color: #0000BB">$link</span><span style="color: #007700">, </span><span style="color: #DD0000">"SELECT DATABASE()"</span><span style="color: #007700">)) {<br /> </span><span style="color: #0000BB">$row </span><span style="color: #007700">= </span><span style="color: #0000BB">mysqli_fetch_row</span><span style="color: #007700">(</span><span style="color: #0000BB">$result</span><span style="color: #007700">);<br /> </span><span style="color: #0000BB">printf</span><span style="color: #007700">(</span><span style="color: #DD0000">"Default database is %s.\n"</span><span style="color: #007700">, </span><span style="color: #0000BB">$row</span><span style="color: #007700">[</span><span style="color: #0000BB">0</span><span style="color: #007700">]);<br /> </span><span style="color: #0000BB">mysqli_free_result</span><span style="color: #007700">(</span><span style="color: #0000BB">$result</span><span style="color: #007700">);<br />}<br /><br /></span><span style="color: #FF8000">/* change db to world db */<br /></span><span style="color: #0000BB">mysqli_select_db</span><span style="color: #007700">(</span><span style="color: #0000BB">$link</span><span style="color: #007700">, </span><span style="color: #DD0000">"world"</span><span style="color: #007700">);<br /><br /></span><span style="color: #FF8000">/* return name of current default database */<br /></span><span style="color: #007700">if (</span><span style="color: #0000BB">$result </span><span style="color: #007700">= </span><span style="color: #0000BB">mysqli_query</span><span style="color: #007700">(</span><span style="color: #0000BB">$link</span><span style="color: #007700">, </span><span style="color: #DD0000">"SELECT DATABASE()"</span><span style="color: #007700">)) {<br /> </span><span style="color: #0000BB">$row </span><span style="color: #007700">= </span><span style="color: #0000BB">mysqli_fetch_row</span><span style="color: #007700">(</span><span style="color: #0000BB">$result</span><span style="color: #007700">);<br /> </span><span style="color: #0000BB">printf</span><span style="color: #007700">(</span><span style="color: #DD0000">"Default database is %s.\n"</span><span style="color: #007700">, </span><span style="color: #0000BB">$row</span><span style="color: #007700">[</span><span style="color: #0000BB">0</span><span style="color: #007700">]);<br /> </span><span style="color: #0000BB">mysqli_free_result</span><span style="color: #007700">(</span><span style="color: #0000BB">$result</span><span style="color: #007700">);<br />}<br /><br /></span><span style="color: #0000BB">mysqli_close</span><span style="color: #007700">(</span><span style="color: #0000BB">$link</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">?></span></span></code></div> </div> </div> <p class="para">The above example will output:</p> <div class="example-contents"><pre><div class="cdata"><pre>Default database is test.Default database is world.</pre></div> </pre></div> </div> <div class="refsect1 seealso"> <h3 class="title">See Also</h3> <p class="para"> <ul class="simplelist"> <li class="member"><a href="mysqli.connect.html" class="function" rel="rdfs-seeAlso">mysqli_connect()</a></li> <li class="member"><a href="mysqli.real-connect.html" class="function" rel="rdfs-seeAlso">mysqli_real_connect()</a></li> </ul> </p> </div></div><hr /><div style="text-align: center;"> <div class="prev" style="text-align: left; float: left;"><a href="mysqli.rollback.html">mysqli::rollback</a></div> <div class="next" style="text-align: right; float: right;"><a href="mysqli.set-charset.html">mysqli::set_charset</a></div> <div class="up"><a href="class.mysqli.html">MySQLi</a></div> <div class="home"><a href="index.html">PHP Manual</a></div></div></body></html>⌨️ 快捷键说明
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