构建销售合同管理功能的企业资源计划（ERP）系统的PHP开发

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

$conn = new mysqli($servername, $username, $password, $dbname);

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

<?php
// 获取表单提交的数据
$contract_id = $_POST['contract_id'];
$contract_date = $_POST['contract_date'];
$contract_amount = $_POST['contract_amount'];
$customer_id = $_POST['customer_id'];

// 插入数据到contract表
$sql = "INSERT INTO contract (contract_id, contract_date, contract_amount, customer_id)
        VALUES ('$contract_id', '$contract_date', '$contract_amount','$customer_id')";

if ($conn->query($sql) === TRUE) {
    echo "合同录入成功";
} else {
    echo "Error: " . $sql . "<br>" . $conn->error;
}

$conn->close();
?>

<?php
// 获取查询条件
$contract_id = $_POST['contract_id'];
$customer_name = $_POST['customer_name'];

// 拼接查询语句
$sql = "SELECT * FROM contract, customer
        WHERE contract.customer_id = customer.customer_id
        AND contract.contract_id = '$contract_id'
        AND customer.customer_name = '$customer_name'";

$result = $conn->query($sql);

if ($result->num_rows > 0) {
    // 输出查询结果
    while($row = $result->fetch_assoc()) {
        echo "合同编号: " . $row["contract_id"]. " - 合同日期: " . $row["contract_date"]. " - 合同金额: " . $row["contract_amount"]. "<br>";
    }
} else {
    echo "查询结果为空";
}

$conn->close();
?>