Let's talk about how to perform descending query in PHP

PHP is a common development language often used to build web applications. In web development, data sorting and querying are very common operations. Descending query is a commonly used way to sort data. This article will introduce how to perform descending query in PHP.

There are two main ways to perform descending query in PHP, namely using database query statements and using PHP array functions for sorting. The specific implementation of these two methods will be introduced below.

1. Use database query statements for descending query

It is very common to perform descending query in the database. This is because the amount of data stored in the database is very large. If you use PHP array Function sorting may take up a lot of memory. Therefore, using database query statements for sorting is a more stable and efficient approach.

The following takes the MySQL database as an example to introduce how to use SQL statements to perform descending queries. First, you need to connect to the database and query the table that needs to be sorted.

//连接数据库
$conn = mysqli_connect("localhost", "root", "password", "database_name");

//查询需要排序的表
$sql = "SELECT * FROM table_name ORDER BY column_name DESC";
$result = mysqli_query($conn, $sql);

In the above code, you will connect to the local MySQL database, query the table named table_name, and sort by descending column name column_name. DESC is the keyword in the SQL statement, indicating descending order, ASC Indicates ascending order. Query results can be accessed using the mysqli_fetch_array() function.

while($row = mysqli_fetch_array($result)) {
  echo $row['column_name'];
}

In the above code, a while loop is used to iterate through the query results and print out the value of a specific column.

2. Use PHP array functions to sort in descending order

If you need to sort in descending order on a small data set, you can use PHP's built-in array functions for sorting. The following describes how to use the arsort() function and the krsort() function to sort in descending order.

• arsort() function

The arsort() function is used to sort the array by value and bind the keys and values ​​together. The order of values ​​will be in descending order. Here is an example:

$num_array = array(3, 6, 1, 9, 2);
arsort($num_array);

foreach($num_array as $num) {
  echo $num . " ";
}

Output result: 9 6 3 2 1

In the above code, first define an array containing numbers. Then, use the arsort() function to sort the array in descending order. Finally, use a foreach loop to iterate through the array and print out each value.

• krsort() function

krsort() function is used to sort the array by key. The order of keys will be in descending order. The following is an example:

$age = array("Peter" => "35", "John" => "40", "Tom" => "25");
krsort($age);

foreach($age as $key => $value) {
  echo "Name: " . $key . " Age: " . $value . " ";
}

Output result: Tom: 25 John: 40 Peter: 35

In the above code, first define an associative array, and then use the krsort() function to sort the key pairs Sort the array in descending order. Finally use a foreach loop to iterate through the associative array and print out each key and value.

Summary

This article introduces how to perform descending query in PHP. Sorting using database queries is a more stable and efficient way, and is suitable for large data sets. If you need to sort on a small data set, you can use the built-in PHP array functions for sorting. Either way, you should choose the best method based on the size of your data set and your query needs.

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