php mysql外键

-- 确保父表有主键
ALTER TABLE parent_table ADD PRIMARY KEY (parent_column);

-- 确保数据类型匹配
ALTER TABLE child_table MODIFY child_column datatype;

-- 使用支持外键的存储引擎，如InnoDB
ALTER TABLE parent_table ENGINE=InnoDB;
ALTER TABLE child_table ENGINE=InnoDB;

ALTER TABLE child_table DROP FOREIGN KEY foreign_key_name;

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

// 创建连接
$conn = new mysqli($servername, $username, $password, $dbname);

// 检查连接
if ($conn->connect_error) {
    die("连接失败: " . $conn->connect_error);
}

// 查询父表
$sql = "SELECT * FROM parent_table";
$result = $conn->query($sql);

if ($result->num_rows > 0) {
    // 输出数据
    while($row = $result->fetch_assoc()) {
        echo "父表ID: " . $row["id"]. " - 父表名称: " . $row["name"]. "<br>";
        
        // 查询子表
        $child_sql = "SELECT * FROM child_table WHERE parent_id = " . $row["id"];
        $child_result = $conn->query($child_sql);
        
        if ($child_result->num_rows > 0) {
            while($child_row = $child_result->fetch_assoc()) {
                echo "子表ID: " . $child_row["id"]. " - 子表名称: " . $child["name"]. "<br>";
            }
        }
    }
} else {
    echo "0 结果";
}
$conn->close();
?>