PHP SQL |在表中查找行，如果不存在，则使用其他表

SELECT * FROM table1 WHERE condition;

<?php
// 连接数据库
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "database";

$conn = new mysqli($servername, $username, $password, $dbname);
if ($conn->connect_error) {
    die("连接失败: " . $conn->connect_error);
}

// 查询表1
$sql = "SELECT * FROM table1 WHERE condition";
$result = $conn->query($sql);

// 如果查询结果为空，则使用其他表进行查询
if ($result->num_rows == 0) {
    $sql = "SELECT * FROM table2 WHERE condition";
    $result = $conn->query($sql);
}

// 处理查询结果
if ($result->num_rows > 0) {
    while($row = $result->fetch_assoc()) {
        // 处理每一行数据
        echo "字段1: " . $row["column1"]. " - 字段2: " . $row["column2"]. "<br>";
    }
} else {
    echo "未找到匹配的行";
}

// 关闭数据库连接
$conn->close();
?>