impala recursive

Impala supports recursive queries using the WITH RECURSIVE syntax. This allows you to write SQL queries that recursively reference a table to perform hierarchical or graph-like operations.

Here's an example of a recursive query in Impala:

WITH RECURSIVE employee_hierarchy AS (
  SELECT id, name, manager_id, 1 AS level
  FROM employees
  WHERE manager_id IS NULL
  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, level
FROM employee_hierarchy
ORDER BY level, name;

In this example, we are selecting all employees and their hierarchical levels in a company. The first part of the query selects the top-level employees (those without a manager), and the second part recursively joins each employee to their manager until the entire hierarchy is traversed.

The result is a table with each employee's ID and name, along with their hierarchical level in the company. The results are ordered by level and name.

Recursive queries can be very powerful for modeling hierarchical or graph-like data. However, they can also be resource-intensive and should be used carefully.