How to use the Teradata recursive query method?

In Teradata, recursive queries can be used to handle data with recursive structure. These queries allow you to reference the same table in a query and use the results from the previous step in each recursive step.

To perform a recursive query in Teradata, you need to use the WITH RECURSIVE clause to define the recursive query and reference the same table within the query. Here is an example of using a recursive query to find all subordinates in an employee table.

Recursive Employee Hierarchy is a basic query to retrieve top-level employees from the Employees table, using EmployeeID 1 as the identifier for the top-level employee.

combine all

Recursive search to retrieve subordinate employees. Retrieve EmployeeID, EmployeeName, and ManagerID from Employees table by joining with EmployeeHierarchy table where ManagerID equals EmployeeID.

In the end, retrieve all subordinate employees by querying the EmployeeHierarchy table.

In the given example, the information of top employees is first retrieved using a basic query, and then the results are combined with the recursive query results using the UNION ALL operator. The recursive query retrieves subordinates from the results of each recursive step and joins them with the employee table. This process continues to iterate recursively until there are no more subordinates left.

Please note that recursive queries must have a termination condition to prevent infinite loops. In the example above, a WHERE clause is used to specify the ID of the top-level employee as the termination condition.

Using Teradata’s recursive queries can easily handle data with recursive structures, but caution must be taken to ensure query performance and accuracy.