How to Best Store and Query Hierarchical Data in SQL?

Efficiently handle hierarchical data structures in SQL databases

There are many methods for modeling and retrieving hierarchical data in databases. One of the commonly used techniques is the Modified Preorder Tree Traversal Algorithm, which simplifies the query of tree data.

There are two main ways to represent hierarchies in a database:

• Nested Set Model (Nested Set): Also known as the improved pre-order traversal algorithm.
• Adjacency List Model: Stores direct parent-child relationships.

Nested Set Algorithm

Nested collection models store hierarchies by assigning each node in the tree a range of values. The range is represented by two fields: left and right. The node's left value is greater than the left values ​​of all its left children and less than the right value of its parent node. Similarly, a node's right value is less than the right values ​​of all its right children and greater than its parent's left value.

Adjacency List Model

The adjacency list model stores hierarchies by representing each node as a row in a table. Each row has two columns: parent_id and node_id. The parent_id column stores the ID of the parent node, while the node_id column stores the ID of the child node.

More resources

For more information, please refer to the following link provided by the Zend Framework community:

• Overview of Nested Set Algorithms
• MySQL Hierarchical Data Management
• Adjacency list database structure
• Comparison of Nested Sets and Adjacency Lists

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