Detailed explanation of various methods for querying all data in PHP tables

In actual project development, it is often necessary to query all data in a table. In response to this need, PHP provides several different methods, which will be described in detail in this article.

1. Use the mysql_query function to query data

The mysql_query function is a very common function that can handle queries, insertions, updates and other operations of the MySQL database. To query all the data in a table, just use the SELECT statement:

$sql = "SELECT * FROM table_name";
$result = mysql_query($sql);

Among them, table_name is the name of the table you want to query, and SELECT * means querying all fields and row data in the table. After the mysql_query function is executed, $result will save the query results, and the data can be read row by row through the mysql_fetch_array function:

while ($row = mysql_fetch_array($result)) {
  // 这里处理每一行数据
}

The mysql_fetch_array function will return an array containing the data of the current row. If there is no more data in the current row, the while loop will stop.

2. Use the mysqli_query function to query data

The mysqli_query function is a new function introduced in PHP5. It has similar functions to the mysql_query function and can also be used to perform MySQL query, insert, and update operations. However, the mysqli_query function is more secure and efficient to use than the mysql_query function, so we recommend using the mysqli_query function. Different from the mysql_query function, the mysqli_query function needs to be connected to the database before it can be used. The following is an example:

$mysqli = new mysqli("localhost", "user", "password", "database_name");
if ($mysqli->connect_error) {
    die("连接失败: " . $mysqli->connect_error);
}

$sql = "SELECT * FROM table_name";
$result = $mysqli->query($sql);

where localhost is the MySQL server address, user and password are the username and password used to connect to the database, and database_name is the name of the database to be connected.

After executing the mysqli_query function, the data can be read line by line through the mysqli_fetch_array function:

while ($row = mysqli_fetch_array($result)) {
   // 这里处理每一行数据
}

The data obtained through the mysqli_fetch_array function is similar to the data obtained by the mysql_fetch_array function.

3. Use PDO to query data

PDO is a popular database access method in PHP. It can interact with a variety of databases, including MySQL, SQLite, PostgreSQL, etc. The steps to use PDO to query data are as follows:

$dsn = "mysql:host=localhost;dbname=mydatabase";
$username = "myusername";
$password = "mypassword";

try {
  $pdo = new PDO($dsn, $username, $password);
} catch (PDOException $e) {
  die("连接失败: " . $e->getMessage());
}

$sql = "SELECT * FROM table_name";
$result = $pdo->query($sql);

It should be noted that, unlike mysqli_query, using PDO requires specifying the database type and host address. In the above code, we are using the MySQL database, localhost is the host address, mydatabase is the name of the database to be connected, myusername and mypassword are the username and password used to connect to MySQL.

After executing the $pdo->query function, you can read data line by line through the fetch and fetchall functions:

while ($row = $result->fetch(PDO::FETCH_ASSOC)) {
  // 这里处理每一行数据
}

The fetch and fetchall functions are similar to the mysql_fetch_array and mysqli_fetch_array functions and can be obtained each row of data.

It should be noted that the PDO function returns an array containing all result rows. Even if the result set has only one row, it is regarded as an array with a length of 1. Only one row of data can be obtained through fetchone.

Summary

The above three methods can query all the data of a table, but their usage methods are slightly different. mysql_query and mysqli_query require a connection to the MySQL server and use mysql_connect or mysqli_connect to connect to the database. PDO can use multiple database types and connect to the server through DSN.

When choosing to use different methods, you should choose based on actual needs and familiarity with different methods in order to achieve the highest development efficiency and database access efficiency.

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