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PHP MySQL SELECT 查询

Created: October-16, 2018

在本教程中，你将学习如何使用 PHP 从 MySQL 表中选择记录。

从数据库表中选择数据

到目前为止，你已经学习了如何创建数据库和表以及插入数据。现在是时候检索前面教程中插入的数据了。SQL SELECT 语句用于从数据库表中选择记录。其基本语法如下：

SELECT column1_name , column2_name , columnN_name FROM table_name ;

让我们使用该 SELECT 语句进行 SQL 查询，之后我们将执行此 SQL 查询，方法是将其传递给 PHP mysqli_query() 函数以检索表数据。

假如我们的 persons 数据库表有以下记录：

+----+------------+-----------+----------------------+
| id | first_name | last_name | email                |
+----+------------+-----------+----------------------+
|  1 | Peter      | Parker    | peterparker@mail.com |
|  2 | John       | Rambo     | johnrambo@mail.com   |
|  3 | Clark      | Kent      | clarkkent@mail.com   |
|  4 | John       | Carter    | johncarter@mail.com  |
|  5 | Harry      | Potter    | harrypotter@mail.com |
+----+------------+-----------+----------------------+

以下示例中的 PHP 代码选择存储在 persons 表中的所有数据 （使用星号字符（*）代替列名称选择表中的所有数据）。

面向过程式

<?php
/* Attempt MySQL server connection. Assuming you are running MySQL
server with default setting (user 'root' with no password) */
$link = mysqli_connect("localhost", "root", "", "demo");
 
// Check connection
if($link === false){
    die("ERROR: Could not connect. " . mysqli_connect_error());
}
 
// Attempt select query execution
$sql = "SELECT * FROM persons";
if($result = mysqli_query($link, $sql)){
    if(mysqli_num_rows($result) > 0){
        echo "<table>";
            echo "<tr>";
                echo "<th>id</th>";
                echo "<th>first_name</th>";
                echo "<th>last_name</th>";
                echo "<th>email</th>";
            echo "</tr>";
        while($row = mysqli_fetch_array($result)){
            echo "<tr>";
                echo "<td>" . $row['id'] . "</td>";
                echo "<td>" . $row['first_name'] . "</td>";
                echo "<td>" . $row['last_name'] . "</td>";
                echo "<td>" . $row['email'] . "</td>";
            echo "</tr>";
        }
        echo "</table>";
        // Free result set
        mysqli_free_result($result);
    } else{
        echo "No records matching your query were found.";
    }
} else{
    echo "ERROR: Could not able to execute $sql. " . mysqli_error($link);
}
 
// Close connection
mysqli_close($link);
?>

面向对象式

<?php
/* Attempt MySQL server connection. Assuming you are running MySQL
server with default setting (user 'root' with no password) */
$mysqli = new mysqli("localhost", "root", "", "demo");
 
// Check connection
if($mysqli === false){
    die("ERROR: Could not connect. " . $mysqli->connect_error);
}
 
// Attempt select query execution
$sql = "SELECT * FROM persons";
if($result = $mysqli->query($sql)){
    if($result->num_rows > 0){
        echo "<table>";
            echo "<tr>";
                echo "<th>id</th>";
                echo "<th>first_name</th>";
                echo "<th>last_name</th>";
                echo "<th>email</th>";
            echo "</tr>";
        while($row = $result->fetch_array()){
            echo "<tr>";
                echo "<td>" . $row['id'] . "</td>";
                echo "<td>" . $row['first_name'] . "</td>";
                echo "<td>" . $row['last_name'] . "</td>";
                echo "<td>" . $row['email'] . "</td>";
            echo "</tr>";
        }
        echo "</table>";
        // Free result set
        $result->free();
    } else{
        echo "No records matching your query were found.";
    }
} else{
    echo "ERROR: Could not able to execute $sql. " . $mysqli->error;
}
 
// Close connection
$mysqli->close();
?>

PDO 式

<?php
/* Attempt MySQL server connection. Assuming you are running MySQL
server with default setting (user 'root' with no password) */
try{
    $pdo = new PDO("mysql:host=localhost;dbname=demo", "root", "");
    // Set the PDO error mode to exception
    $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
} catch(PDOException $e){
    die("ERROR: Could not connect. " . $e->getMessage());
}
 
// Attempt select query execution
try{
    $sql = "SELECT * FROM persons";   
    $result = $pdo->query($sql);
    if($result->rowCount() > 0){
        echo "<table>";
            echo "<tr>";
                echo "<th>id</th>";
                echo "<th>first_name</th>";
                echo "<th>last_name</th>";
                echo "<th>email</th>";
            echo "</tr>";
        while($row = $result->fetch()){
            echo "<tr>";
                echo "<td>" . $row['id'] . "</td>";
                echo "<td>" . $row['first_name'] . "</td>";
                echo "<td>" . $row['last_name'] . "</td>";
                echo "<td>" . $row['email'] . "</td>";
            echo "</tr>";
        }
        echo "</table>";
        // Free result set
        unset($result);
    } else{
        echo "No records matching your query were found.";
    }
} catch(PDOException $e){
    die("ERROR: Could not able to execute $sql. " . $e->getMessage());
}
 
// Close connection
unset($pdo);
?>

代码解释

在上面的示例中， mysqli_query() 函数返回的数据存储在 $result 变量中。每次 mysqli_fetch_array() 调用时，它都会将结果的下一行作为数组返回。该 while 循环 在结果集合的所有行进行遍历。最后，可以通过将字段索引或字段名称传递给 $row 变量，例如 $row['id'] 或 $row[0] ， $row['first_name'] 或 $row[1] ， $row['last_name'] 或 $row[2] ，$row['email'] 或 $row[3]，从行访问单个字段的值。

如果要使用 for 循环 ，可以通过将变量 $result 传递给 mysqli_num_rows() 函数来获取循环计数器值或查询返回的行数。此循环计数器值确定循环应运行的次数。