Скачать или смотреть How to Achieve Recursive Query Results in MySQL 5.X Without Native Support

Learn how to handle recursive queries in MySQL 5.X using functions and unions to extract hierarchical data from your employee table effectively.
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Mastering Recursive Queries in MySQL 5.X: A Guide for Hierarchical Data

When dealing with hierarchical data in databases, recursive queries are often essential to navigate parent-child relationships efficiently. However, if you're using MySQL 5.x, you're at a disadvantage since it lacks built-in support for recursive Common Table Expressions (CTEs) introduced in MySQL 8.0. This guide will guide you through techniques to achieve similar outcomes in earlier versions without direct recursive functionality.

Understanding the Problem

Consider a scenario where you have an emp table representing an organizational structure, where each employee can have a manager (or boss). You'd like to retrieve a list of employees along with their respective bosses and identify the hierarchy levels.

Here's an example of the desired output structure:

ENAMEBOSSEMPNOPRIORNAMELEVELKINGNULL78391JONES78397566KING2BLAKE78397698KING2...............To accomplish this, you must devise a way to mimic recursive behavior.

Solution Approaches

Approach 1: Using User-Defined Functions

One viable method is to write MySQL User-Defined Functions (UDFs) that can handle logic for determining PRIORNAME and LEVEL values. Below is a structured approach to achieve this.

Create User-Defined Functions:

Create functions such as udf_emp_priorname(empno) to fetch the name of the manager and udf_emp_level(empno) to determine the employee's level in the hierarchy.

Construct the SQL Query:
Utilize these functions within your SQL query to retrieve the required data.

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Approach 2: Using Union of Queries

If you're unable to utilize functions, another approach is to concatenate results from various queries that sequentially return data for different levels. Here’s how you can do it:

Level 1 Employees: Fetch employees who do not have a manager.

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Level 2 Employees: Join on the first level to get employees managed by those at the first level.

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Level 3 Employees: Continue in this manner for subsequent levels.

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Final Thoughts

Handling hierarchical data in MySQL 5.x can be challenging without recursive CTE support. However, with a bit of creativity using user-defined functions and union queries, you can effectively extract and present your employee hierarchy.

By following these methods, you can ensure that you retrieve the organizational structure accurately, displaying relationship details in a clear and organized format.

If you're still wrestling with your MySQL queries or need further assistance, don't hesitate to reach out. Happy querying!