How to use the release query resource function in php

PHP is a widely used server-side scripting language commonly used for web development. In the process of web development, database query function is often used. After querying the database, the query resources must be released in time in order to release resources and avoid memory leaks. This article will introduce how to use the release query resource function in PHP.

1. mysql_free_result function

The mysql_free_result function can release the memory occupied by the result set. The syntax of this function is as follows:

bool mysql_free_result(resource $result)

This function receives a result set and releases its memory. Note that this function can only be called when the result set is no longer used, otherwise errors such as "MySQL server has gone away" will appear.

The following is an example of using the mysql_free_result function:

$link = mysql_connect("localhost", "mysql_user", "mysql_password");
mysql_select_db("my_db");
$result = mysql_query("SELECT * FROM my_table");
while ($row = mysql_fetch_array($result)) {
    echo $row[0];
    echo $row[1];
    echo $row[2];
}
mysql_free_result($result);
mysql_close($link);

In this example, we first connect to the MySQL server and select the database. Then execute the SELECT statement to query all data in the table. Then use a while loop to iterate through each row and release the memory used by the result set. Finally, close the connection to the MySQL server.

2. mysqli_free_result function

The mysqli_free_result function is similar to the mysql_free_result function, but the difference is that it works with the mysqli extension. The syntax of this function is as follows:

bool mysqli_free_result(mysqli_result $result)

This function receives a result set of type mysqli_result and releases its memory. Like the mysql_free_result function, this function can only be called when the result set is no longer used.

The following is an example of using the mysqli_free_result function:

$mysqli = new mysqli("localhost", "mysql_user", "mysql_password", "my_db");
$result = $mysqli->query("SELECT * FROM my_table");
while ($row = $result->fetch_row()) {
    echo $row[0];
    echo $row[1];
    echo $row[2];
}
mysqli_free_result($result);
$mysqli->close();

In this example, we use the mysqli extension to connect to the database, execute the SELECT statement to query all the data in the table, and use a while loop to traverse every line. The memory used by the result set is then released and the connection to the MySQL server is closed.

3. pg_free_result function

The pg_free_result function is suitable for connecting to a PostgreSQL database. The syntax of this function is as follows:

bool pg_free_result(resource $result)

This function receives a result set and releases its memory. Like the previous two functions, this function can only be called when the result set is no longer used.

Here is an example using the pg_free_result function:

$conn = pg_connect("host=localhost port=5432 dbname=mydb user=postgres password=mypass");
$result = pg_query($conn, "SELECT * FROM mytable");
while ($row = pg_fetch_array($result)) {
    echo $row[0];
    echo $row[1];
    echo $row[2];
}
pg_free_result($result);
pg_close($conn);

In this example, we connect to the PostgreSQL database and select the database mydb. Then execute the SELECT statement to query all data in the table. Use a while loop to iterate through each row and release the memory used by the result set. Finally, close the connection to the PostgreSQL server.

Summary:

In the process of Web development, querying the database is essential. As the amount of data increases, the memory used by the query also increases. In order to avoid memory leaks, resources used by queries must be released in a timely manner. PHP provides a series of functions to facilitate the release of query resources after we have finished using them, including mysql_free_result, mysqli_free_result and pg_free_result. Proficient in using these functions can avoid many common database query errors.

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