How to Fetch Nested Categories Recursively with a Single SQL Query?

Fetching Nested Categories with a Single Query

In a website with articles organized into hierarchical sections, retrieving these sections efficiently is crucial. This question explores how to fetch categories recursively with a single SQL query using PHP and MySQL.

To build a recursive tree structure in PHP, the following approach is proposed:

• Create an Array of Node References:

  • Query the database for all categories, including their IDs, names, and parent IDs.
  • Create an associative array where each node represents a category and its children are represented by an empty array.

• Populate the Tree Structure:

  • Iterate over the node array.

  • For each node, check if its parent ID exists in the node list.

    • If the parent exists, add the current node as a child toその parent's children list.
    • Otherwise, add the current node as a top-level node in the tree.

• Remove Temporary Arrays:

  • Once the tree structure is complete, remove the node list and unset any references.

This approach allows you to build a hierarchical tree in pure PHP, providing faster and more efficient data retrieval compared to iterative queries in MySQL. The final tree structure will be stored in the $tree array, with each category and its children represented.

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