Note that the order of arguments for `mysqli_select_db` is opposite what it is for the deprecated `mysql_select_db`.
(PHP 5, PHP 7, PHP 8)
mysqli::select_db -- mysqli_select_db — 选择用于数据库查询的默认数据库
面向对象风格
$database): bool过程化风格
选择默认数据库，用于在已连接的数据库中执行查询。
注意:
此函数只能用于更改连接的默认数据库。可以在 mysqli_connect() 中使用第 4 个参数选择默认数据库。
成功时返回 true， 或者在失败时返回 false。
If mysqli error reporting is enabled (MYSQLI_REPORT_ERROR) and the requested operation fails,
a warning is generated. If, in addition, the mode is set to MYSQLI_REPORT_STRICT,
a mysqli_sql_exception is thrown instead.
示例 #1 mysqli::select_db() 示例
面向对象风格
<?php
mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT);
$mysqli = new mysqli("localhost", "my_user", "my_password", "test");
/* get the name of the current default database */
$result = $mysqli->query("SELECT DATABASE()");
$row = $result->fetch_row();
printf("Default database is %s.\n", $row[0]);
/* change default database to "world" */
$mysqli->select_db("world");
/* get the name of the current default database */
$result = $mysqli->query("SELECT DATABASE()");
$row = $result->fetch_row();
printf("Default database is %s.\n", $row[0]);过程化风格
<?php
mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT);
$link = mysqli_connect("localhost", "my_user", "my_password", "test");
/* get the name of the current default database */
$result = mysqli_query($link, "SELECT DATABASE()");
$row = mysqli_fetch_row($result);
printf("Default database is %s.\n", $row[0]);
/* change default database to "world" */
mysqli_select_db($link, "world");
/* get the name of the current default database */
$result = mysqli_query($link, "SELECT DATABASE()");
$row = mysqli_fetch_row($result);
printf("Default database is %s.\n", $row[0]);以上示例会输出：
Default database is test. Default database is world.
Note that the order of arguments for `mysqli_select_db` is opposite what it is for the deprecated `mysql_select_db`.