PHP mysqli_select_db()用法及代码示例

定义和用法

这个mysqli_select_db()函数接受一个表示现有数据库的字符串值，并将其作为默认数据库。

用法

mysqli_select_db($con, name)

参数

Sr.No	参数及说明
1	con(Mandatory) 这是一个表示与 MySQL 服务器的连接的对象。
2	name(Mandatory) 这是一个字符串值，表示您需要将其设为默认数据库的现有数据库的名称。

返回值

PHP mysqli_select_db() 函数返回一个布尔值，如果操作成功则为真，否则为假。

PHP版本

这个函数最初是在 PHP 版本 5 中引入的，适用于所有后续版本。

示例

以下示例演示了 mysqli_select_db() 函数的用法(程序风格) -

<?php
   //Creating a connection
   $con = mysqli_connect("localhost", "root", "password", "mydb");

   //Selecting the database
   mysqli_query($con, "CREATE DATABASE NewDatabase");
   mysqli_select_db($con, "NewDatabase");

   //Retrieving the current database name
   $res = mysqli_query($con, "SELECT DATABASE()");

   while ($row = mysqli_fetch_row($res)) {
      print("Current Database:".$row[0]);
   }

   //Closing the connection
   mysqli_close($con);
?>

这将产生以下结果 -

Current Database:newdatabase

示例

在面向对象的风格中，这个函数的语法是 $con->select_db();以下是面向对象样式 $minus 中此函数的示例；

<?php
   //Creating a connection
   $con = new mysqli("localhost", "root", "password", "mydb");

   //Retrieving the current database name
   $res = $con->query("SELECT DATABASE()");
   while ($row = $res->fetch_row()) {
      print("Initial Database:".$row[0]."\n");
   }

   //Selecting the database
   $con->query("CREATE DATABASE NewDatabase");
   $con->select_db("NewDatabase");

   //Retrieving the current database name
   $res = $con->query("SELECT DATABASE()");

   while ($row = $res->fetch_row()) {
      print("Current Database:".$row[0]);
   }

   //Closing the connection
   $res = $con -> close();
?>

这将产生以下结果 -

Initial Database:mydb
Current Database:newdatabase

示例

除了在连接时指定数据库，您也可以稍后使用此函数选择它，如下所示 -

<?php
   //Creating a connection
   $con = mysqli_connect("localhost", "root", "password");

   //Selecting the database
   mysqli_select_db($con, "mydb");
   print("Database Selected ..."."\n");

   mysqli_query($con, "CREATE TABLE IF NOT EXISTS my_team(ID INT, First_Name VARCHAR(255), Last_Name VARCHAR(255), Place_Of_Birth VARCHAR(255), Country VARCHAR(255))");
   print("Table Created ..."."\n");

   //Inserting a records into the my_team table
   mysqli_query($con, "insert into my_team values(1, 'Shikhar', 'Dhawan', 'Delhi', 'India')");
   mysqli_query($con, "insert into my_team values(2, 'Jonathan', 'Trott', 'CapeTown', 'SouthAfrica')");
   mysqli_query($con, "insert into my_team values(3, 'Kumara', 'Sangakkara', 'Matale', 'Srilanka')");
   mysqli_query($con, "insert into my_team values(4, 'Virat', 'Kohli', 'Delhi', 'India')");

   print("Records Inserted ..."."\n");
 
   //Closing the connection
   mysqli_close($con);
?>

这将产生以下结果 -

Database Selected ...
Table Created ...
Records Inserted ...

示例

<?php
   $connection_mysql = mysqli_connect("localhost", "root", "password","mydb");
   
   if (mysqli_connect_errno($connection_mysql)){
      echo "Failed to connect to MySQL:" . mysqli_connect_error();
   }
   
   $res = mysqli_select_db($connection_mysql,"testdb");
   
   if($res){
	   echo "Database Selected";
   }else{
	   echo "Error Occurred";
   }
   
   mysqli_close($connection_mysql);

?>

这将产生以下结果 -

Database Selected