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Recursive Queries

Introduction
The very basics
Infinite looping
11. LIMIT keyword
Processing graphs with recursive CTE
Summary

Instruction

As you could see, our query terminated with an error, but it's only because of the special database settings in our course. Normally, the database would not stop the query on its own. As a result, it would freeze and you would have to break the query manually. Please remember about that!

In Postgres, you can use another keyword LIMIT n, where n is the maximal number of rows you expect. Even if your query does not contain a termination check (or it does, but the check is faulty), LIMIT will take care of query termination:

WITH RECURSIVE counter(previous_value) AS (
  SELECT
    1 -- anchor member
  UNION ALL
  SELECT
    previous_value + 1 -- recursive member
  FROM counter
)

SELECT 
  * 
FROM counter -- invocation
LIMIT 10; -- termination check

Exercise

Run the template query with LIMIT and see for yourself how it works.