In this tutorial, we will learn How to create a MySQL hierarchical recursive query which is also called as CTE ( Common Table Expressions) moreover for achieving it we can also use CTE and UNION All statements for a recursive query that has a self-referencing foreign key relationship.
Moreover, we have given an example here with a pseudo code that can be helping you for getting the topic more clearly and use it in our project.
WITH RECURSIVE employee_hierarchy AS ( SELECT id, name, manager_ id, 1 AS level FROM employees WHERE manager_ id IS NULL -- start at the root level UNION ALL SELECT e. id, e. name, e. manager_ id, eh. level + 1 FROM employees e JOIN employee_ hierarchy eh ON e. manager_ id = eh .id ) SELECT id, name, manager _id, level FROM employee_ hierarchy ORDER BY level, name;
In the given above example we created firs a CTE with the name as employee hierarchy that has contained two select statements that are separated with a Union all Statements, As mentioned we use it for getting Hierarchical Recursion. Here each ‘select’ has a different role to play which we will elaborate on here.
The first select statement is used for selecting the root level employee( Here root level refers to the employees who do not have any manager above in rank), And after that, we has used the second ‘select’ statement which is used for selecting the child or lower rank employees or we can all the employees except the employees selected earlier, though joining the employee table to the CTE that is simply based on manager id that is already defined as a foreign key.
Here the level column is used for keeping a record of the depth of each and every employee in the same hierarchy which is assigned. Once the CTE is defined, we select the columns from the CTE and order the results by the Level and name columns. This produces a hierarchy recursion query result that shows all employees in the hierarchy, sorted by their level and name.
Note that recursion queries can be resource-intensive, especially on large tables with deep hierarchies. It’s important to consider the performance implications and use appropriate indexes on the foreign key column for optimal performance.
To learn more about How To Create A MySQL Hierarchical Recursive Query you may also visit: by Sack overflow.
To learn more about MySQL tutorials and the solutions of the problems that could be faced during executing the SQL program and these posts could be very useful ways to get the concepts visit: MySQL Tutorials And Problems.