How to Efficiently Encode MySQL Query Results into JSON using PHP?

JSON Encoding MySQL Query Results

When working with MySQL results, it's often necessary to convert them into JSON format for use in web applications or other contexts. In PHP, the built-in json_encode() function is commonly used for this purpose. Let's explore how to utilize json_encode() with MySQL query results.

Iterating vs. Direct Encoding

One approach is to iterate through each row of the query results and apply json_encode() to each row individually. This can be done using a while or foreach loop:

$sth = mysqli_query($conn, "SELECT ...");
$rows = [];
while($r = mysqli_fetch_assoc($sth)) {
    $rows[] = json_encode($r);
}

This method allows for fine-grained control over the JSON output, but it can be inefficient for large result sets.

Direct Encoding of the Results Object

Another approach is to directly encode the entire results object, which returns a JSON string representation of all the rows in a single call:

$sth = mysqli_query($conn, "SELECT ...");
$rows = mysqli_fetch_all($sth, MYSQLI_ASSOC);
$json = json_encode($rows);

Using this method is more efficient for large result sets, as it eliminates the need to iterate through each row and encode it separately.

Requirements

To use json_encode() with MySQL query results, ensure the following requirements are met:

• PHP version 5.2 or higher
• Php-json package installed and loaded

Alternative approaches

Modern PHP versions also support the mysqli_fetch_all() function, which can fetch all rows from a result set into an array in one go. This array can then be directly encoded into JSON:

$result = mysqli_query($conn, "SELECT ...");
$rows = mysqli_fetch_all($result);
$json = json_encode($rows);

By using mysqli_fetch_all(), you can improve the efficiency of JSON encoding for large result sets.

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