mysqli_select_db()函數(shù)用于更改連接的默認(rèn)數(shù)據(jù)庫。
mysqli_select_db()函數(shù)接受表示現(xiàn)有數(shù)據(jù)庫的字符串值，并將其作為默認(rèn)數(shù)據(jù)庫。
mysqli_select_db($con, name)
| 序號 | 參數(shù)及說明 |
|---|---|
| 1 | con(必需) 這是一個表示與MySQL Server的連接的對象。 |
| 2 | name(必需) 這是一個字符串值，表示數(shù)據(jù)庫名稱。 |
PHP mysqli_select_db()函數(shù)返回一個布爾值，如果操作成功，則為true，否則為false。
此函數(shù)最初是在PHP版本5中引入的，并且可以在所有更高版本中使用。
以下示例演示了mysqli_select_db()函數(shù)的用法（面向過程風(fēng)格）-
<?php
//建立連接
$con = mysqli_connect("localhost", "root", "password", "mydb");
//選擇數(shù)據(jù)庫
mysqli_query($con, "CREATE DATABASE NewDatabase");
mysqli_select_db($con, "NewDatabase");
//檢索當(dāng)前數(shù)據(jù)庫名稱
$res = mysqli_query($con, "SELECT DATABASE()");
while ($row = mysqli_fetch_row($res)) {
print("當(dāng)前數(shù)據(jù)庫: ".$row[0]);
}
//關(guān)閉連接
mysqli_close($con);
?>輸出結(jié)果
當(dāng)前數(shù)據(jù)庫: newdatabase
在面向?qū)ο箫L(fēng)格中，此函數(shù)的語法為$con->select_db();。以下是面向?qū)ο箫L(fēng)格中此函數(shù)的示例；
<?php
//建立連接
$con = new mysqli("localhost", "root", "password", "mydb");
//檢索當(dāng)前數(shù)據(jù)庫名稱
$res = $con->query("SELECT DATABASE()");
while ($row = $res->fetch_row()) {
print("初始數(shù)據(jù)庫: ".$row[0]."\n");
}
//選擇數(shù)據(jù)庫
$con->query("CREATE DATABASE NewDatabase");
$con->select_db("NewDatabase");
//檢索當(dāng)前數(shù)據(jù)庫名稱
$res = $con->query("SELECT DATABASE()");
while ($row = $res->fetch_row()) {
print("當(dāng)前數(shù)據(jù)庫: ".$row[0]);
}
//關(guān)閉連接
$res = $con -> close();
?>輸出結(jié)果
初始數(shù)據(jù)庫: mydb 當(dāng)前數(shù)據(jù)庫: newdatabase
除了在連接時指定數(shù)據(jù)庫，您還可以稍后使用此函數(shù)更改連接的默認(rèn)數(shù)據(jù)庫，如下所示：
<?php
//建立連接
$con = mysqli_connect("localhost", "root", "password");
//選擇數(shù)據(jù)庫
mysqli_select_db($con, "mydb");
print("選擇數(shù)據(jù)庫 ..."."\n");
mysqli_query($con, "CREATE TABLE IF NOT EXISTS my_team(ID INT, First_Name VARCHAR(255), Last_Name VARCHAR(255), Place_Of_Birth VARCHAR(255), Country VARCHAR(255))");
print("創(chuàng)建表 ..."."\n");
//將記錄插入到my_team表中
mysqli_query($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($con, "insert into my_team values(4, 'Virat', 'Kohli', 'Delhi', 'India')");
print("插入記錄 ..."."\n");
//關(guān)閉連接
mysqli_close($con);
?>輸出結(jié)果
選擇數(shù)據(jù)庫 ... 創(chuàng)建表 ... 插入記錄 ...
更改連接的默認(rèn)數(shù)據(jù)庫：
<?php
$connection_mysql = mysqli_connect("localhost", "root", "password","mydb");
if (mysqli_connect_errno($connection_mysql)){
echo "連接MySQL失敗: " . mysqli_connect_error();
}
$res = mysqli_select_db($connection_mysql,"testdb");
if($res){
echo "選擇的數(shù)據(jù)庫";
}else{
echo "發(fā)生錯誤";
}
mysqli_close($connection_mysql);
?>輸出結(jié)果
選擇的數(shù)據(jù)庫