PHP MySQL 使用 WHERE 子句

从 MySQL 数据库中选择和过滤数据

WHERE 子句用于过滤记录。

WHERE 子句用于仅提取满足指定条件的记录。

SELECT column_name(s) FROM table_name WHERE column_name operator value

要了解有关 SQL 的更多信息，请访问我们的SQL教程。

使用 MySQLi 选择和过滤数据

以下示例从 MyGuests 表（其中姓氏为 "Doe"）中选择 id、firstname 和 lastname 列，并将其显示在页面上：

示例（MySQLi 面向对象）

<?php
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDB";

// Create connection
$conn = new mysqli($servername, $username, $password, $dbname);
// Check connection
if ($conn->connect_error) {
  die("Connection failed: " . $conn->connect_error);
}

$sql = "SELECT id, firstname, lastname FROM MyGuests WHERE lastname='Doe'";
$result = $conn->query($sql);

if ($result->num_rows > 0) {
  // output data of each row
  while($row = $result->fetch_assoc()) {
    echo "id: " . $row["id"]. " - Name: " . $row["firstname"]. " " . $row["lastname"]. "<br>";
  }
} else {
  echo "0 results";
}
$conn->close();
?>

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从上面的例子中解释的代码行：

首先，我们设置 SQL 查询，从 MyGuests 表中选择 id、名字和姓氏列，其中姓氏为 "Doe"。下一行代码运行查询并将结果数据放入名为 $result 的变量中。

然后，function num_rows()检查返回的行数是否超过零。

如果返回的行数多于零，则该函数fetch_assoc()将所有结果放入一个我们可以循环遍历的关联数组中。这while()循环遍历结果集并输出 id、firstname 和 lastname 列中的数据。

以下示例以 MySQLi 过程方式显示与上面示例相同的内容：

示例（MySQLi 过程）

<?php
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDB";

// Create connection
$conn = mysqli_connect($servername, $username, $password, $dbname);
// Check connection
if (!$conn) {
die("Connection failed: " . mysqli_connect_error());
}

$sql = "SELECT id, firstname, lastname FROM MyGuests WHERE lastname='Doe'";
$result = mysqli_query($conn, $sql);

if (mysqli_num_rows($result) > 0) {
  // output data of each row
while($row = mysqli_fetch_assoc($result)) {
    echo "id: " . $row["id"]. " - Name: " . $row["firstname"]. " " . $row["lastname"]. "<br>";
}
} else {
  echo "0 results";
}

mysqli_close($conn);
?>

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您还可以将结果放入 HTML 表格中：

示例（MySQLi 面向对象）

<?php
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDB";

// Create connection
$conn = new mysqli($servername, $username, $password, $dbname);
// Check connection
if ($conn->connect_error) {
  die("Connection failed: " . $conn->connect_error);
}

$sql = "SELECT id, firstname, lastname FROM MyGuests WHERE lastname='Doe'";
$result = $conn->query($sql);

if ($result->num_rows > 0) {
  echo "<table><tr><th>ID</th><th>Name</th></tr>";
// output data of each row
  while($row = $result->fetch_assoc()) {
    echo "<tr><td>".$row["id"]."</td><td>".$row["firstname"]." ".$row["lastname"]."</td></tr>";
  }
  echo "</table>";
} else {
echo "0 results";
}
$conn->close();
?>

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使用 PDO 选择数据（+ 准备好的语句）

以下示例使用准备好的语句。

它从 MyGuests 表（其中姓氏为 "Doe"）中选择 id、名字和姓氏列，并将其显示在 HTML 表中：

示例（PDO）

<?php
echo "<table style='border: solid 1px black;'>";
echo "<tr><th>Id</th><th>Firstname</th><th>Lastname</th></tr>";

class TableRows extends RecursiveIteratorIterator {
function __construct($it) {
    parent::__construct($it, self::LEAVES_ONLY);
}

function current() {
    return "<td style='width:150px;border:1px solid black;'>" . parent::current(). "</td>";
  }

  function beginChildren() {
    echo "<tr>";
  }

function endChildren() {
    echo "</tr>" . "\n";
  }
}

$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDBPDO";

try {
  $conn = new PDO("mysql:host=$servername;dbname=$dbname", $username, $password);
$conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
  $stmt = $conn->prepare("SELECT id, firstname, lastname FROM MyGuests WHERE lastname='Doe'");
  $stmt->execute();

// set the resulting array to associative
$result = $stmt->setFetchMode(PDO::FETCH_ASSOC);
  foreach(new TableRows(new RecursiveArrayIterator($stmt->fetchAll())) as $k=>$v) {
    echo $v;
  }
}
catch(PDOException $e) {
  echo "Error: " . $e->getMessage();
}
$conn = null;
echo "</table>";
?>

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