PostgreSQL Recursive View

Summary: in this tutorial, you will learn how to create a PostgreSQL recursive view using the CREATE RECURSIVE VIEW statement.

Introduction to the PostgreSQL recursive view

PostgreSQL 9.3 added a new syntax for creating recursive views specified in the standard SQL. The CREATE RECURSIVE VIEW statement is syntax sugar for a standard recursive query.

The following illustrates the CREATE RECURSIVE VIEW syntax:

CREATE RECURSIVE VIEW view_name(columns) AS
SELECT columns;
Code language: SQL (Structured Query Language) (sql)

First, specify the name of the view that you want to create in the CREATE RECURSIVE VIEW clause. You can add an optional schema-qualified to the name of the view.

Second, add the SELECT statement to query data from base tables. The SELECT statement references the view_name to make the view recursive.

This statement above is equivalent to the following statement:

CREATE VIEW view_name 
AS
  WITH RECURSIVE cte_name (columns) AS (
    SELECT ...)
  SELECT columns FROM cte_name;
Code language: SQL (Structured Query Language) (sql)

Creating recursive view example

We will use the employees table created in the recursive query tutorial for the demonstration.

The following recursive query returns the employee and their managers up to the CEO level using a common table expression or CTE.

WITH RECURSIVE reporting_line AS (
	SELECT
		employee_id,
		full_name AS subordinates
	FROM
		employees
	WHERE
		manager_id IS NULL
	UNION ALL
		SELECT
			e.employee_id,
			(
				rl.subordinates || ' > ' || e.full_name
			) AS subordinates
		FROM
			employees e
		INNER JOIN reporting_line rl ON e.manager_id = rl.employee_id
) SELECT
	employee_id,
	subordinates
FROM
	reporting_line
ORDER BY
	employee_id;
Code language: SQL (Structured Query Language) (sql)

 employee_id |                         subordinates
-------------+--------------------------------------------------------------
           1 | Michael North
           2 | Michael North > Megan Berry
           3 | Michael North > Sarah Berry
           4 | Michael North > Zoe Black
           5 | Michael North > Tim James
           6 | Michael North > Megan Berry > Bella Tucker
           7 | Michael North > Megan Berry > Ryan Metcalfe
           8 | Michael North > Megan Berry > Max Mills
           9 | Michael North > Megan Berry > Benjamin Glover
          10 | Michael North > Sarah Berry > Carolyn Henderson
          11 | Michael North > Sarah Berry > Nicola Kelly
          12 | Michael North > Sarah Berry > Alexandra Climo
          13 | Michael North > Sarah Berry > Dominic King
          14 | Michael North > Zoe Black > Leonard Gray
          15 | Michael North > Zoe Black > Eric Rampling
          16 | Michael North > Megan Berry > Ryan Metcalfe > Piers Paige
          17 | Michael North > Megan Berry > Ryan Metcalfe > Ryan Henderson
          18 | Michael North > Megan Berry > Max Mills > Frank Tucker
          19 | Michael North > Megan Berry > Max Mills > Nathan Ferguson
          20 | Michael North > Megan Berry > Max Mills > Kevin Rampling
(20 rows)
Code language: SQL (Structured Query Language) (sql)

You can use the CREATE RECURSIVE VIEW statement to convert the query into a recursive view as follows:

CREATE RECURSIVE VIEW reporting_line (employee_id, subordinates) AS 
SELECT
	employee_id,
	full_name AS subordinates
FROM
	employees
WHERE
	manager_id IS NULL
UNION ALL
	SELECT
		e.employee_id,
		(
			rl.subordinates || ' > ' || e.full_name
		) AS subordinates
	FROM
		employees e
	INNER JOIN reporting_line rl ON e.manager_id = rl.employee_id;
Code language: SQL (Structured Query Language) (sql)

To see the reporting line of the employee id 10, you query directly from the view:

SELECT
	subordinates
FROM
	reporting_line
WHERE
	employee_id = 10;
Code language: SQL (Structured Query Language) (sql)

                  subordinates
-------------------------------------------------
 Michael North > Sarah Berry > Carolyn Henderson
(1 row)
Code language: SQL (Structured Query Language) (sql)

In this tutorial, you have learned how to create PostgreSQL recursive view based on a recursive query.