To use PHP for MySQL web development, you must first master the connection to the database, perform query and data operations. 1. It is recommended to use mysqli extension to connect to the database. Create a connection through new mysqli() and check whether it is successful; 2. Use query() method to execute SQL queries, combine fetch_assoc() to traverse the result set, and pay attention to prevent preprocessing statements from being used to prevent SQL injection; 3. When inserting or updating data, use prepare() and bind_param() to bind parameters to ensure safe transmission of values; 4. Common errors include connection failure, query results, insertion conflicts, etc. You can troubleshoot problems by checking configuration, field names, constraint restrictions and opening error prompts. Mastering these basic operations can meet most PHP MySQL development needs.
If you plan to use PHP for web development, you can't avoid MySQL. PHP and MySQL are very common, and frameworks such as WordPress and Laravel are based on their combination. But when you first start learning, you may feel a little confused about connecting to the database and operating data. Don't worry, I will take you step by step to clarify how to use MySQL in PHP.
How to connect to a MySQL database?
If you want to operate the database, the first step is to connect it. PHP provides a variety of ways to connect MySQL, the most commonly used are mysqli and PDO . mysqli is recommended here because it is designed for MySQL and has simple syntax.
The basic writing method is as follows:
$host = 'localhost';
$user = 'root';
$pass = '';
$dbname = 'test_db';
$conn = new mysqli($host, $user, $pass, $dbname);
if ($conn->connect_error) {
die("Connection failed:" . $conn->connect_error);
}Pay attention to a few points:
- The host name is usually localhost;
- The user name and password must be filled in according to your own database configuration;
- If the connection is not up, first check whether the database is started, and then confirm whether the account password is correct.
How to execute SQL query?
After the connection is successful, the query statement can be executed. For example, if you want to get all user information from a table called users , you can write it like this:
$sql = "SELECT id, name, email FROM users";
$result = $conn->query($sql);
if ($result->num_rows > 0) {
while($row = $result->fetch_assoc()) {
echo "ID: " . $row['id'] . " - Name: " . $row['name'] . "<br>";
}
} else {
echo "no result";
}This example does a few things:
- Write a SELECT query;
- After execution, determine whether there is a return result;
- If so, output data one by one;
- If there is no, it means "no result".
Note: SQL injection is a security risk. If the content input by the user is directly spliced ??into SQL, it is easy to be attacked. At this time, prepared statements should be used, such as
mysqli_prepare()or PDO's binding parameter function.
What should you pay attention to when inserting and updating data?
In addition to checking data, we often have to insert new records or modify existing records. For example, register a new user:
$stmt = $conn->prepare("INSERT INTO users (name, email) VALUES (?, ?)");
$stmt->bind_param("ss", $name, $email);
$name = "Zhang San";
$email = "zhangsan@example.com";
$stmt->execute();
echo "New user added successfully";
$stmt->close();Preprocessing statements are used here, which is beneficial to prevent SQL injection and facilitate parameter transmission. If you update the data, the structure is similar, but SQL is changed to UPDATE:
UPDATE users SET email = ? WHERE id = ?
Then remember to bind the parameter order to make sure the variable types match.
Common errors and troubleshooting suggestions
When you first get started, you can easily encounter some problems. for example:
- The database connection cannot be made: check whether the user name, password, and database exist;
- The query has no result, but there is clearly: it may be that the field name is written incorrectly, or the conditions are not met;
- Failed to insert data: see if there is a limit on the field length, or whether a unique constraint conflict is set;
- The page is blank and there is no error: Open PHP error message and add
display_errors=Onto php.ini.
In addition, it is recommended to use var_dump() or print_r() to view the variable content, which is helpful for debugging.
Basically that's it. MySQL is very basic in PHP projects. By mastering the actions of connection, query, addition, deletion and modification, you can meet most needs. It may be a bit confusing at the beginning, but it will be much easier to practice a few more times.
The above is the detailed content of mysql tutorial for PHP web development. For more information, please follow other related articles on the PHP Chinese website!
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