Recursive CTE concept in SQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a Recursive CTE in SQL?

A Recursive CTE (Common Table Expression) is a query that refers to itself to repeatedly execute and build a result set step-by-step, often used to work with hierarchical or tree-structured data.

beginner

What are the two main parts of a Recursive CTE?

1. Anchor member: The starting query that runs once.<br>2. Recursive member: The part that references the CTE itself to repeat and build on the results.

intermediate

Why do Recursive CTEs need a termination condition?

To stop the recursion from running forever, a condition limits how many times the recursive part runs, usually by checking when no new rows are added.

beginner

Give a simple real-life example where Recursive CTEs are useful.

Finding all employees under a manager in a company hierarchy, where each employee can have subordinates, and you want to list everyone below a certain manager.

beginner

What SQL keyword is used to define a Recursive CTE?

The keyword WITH is used to start a CTE, and the RECURSIVE keyword (in some SQL dialects like PostgreSQL) indicates that the CTE is recursive.

What does the anchor member of a Recursive CTE do?

A Starts the recursion with initial rows

B Terminates the recursion

C Joins two tables

D Deletes rows from a table

The anchor member runs once to provide the initial rows for the recursion.

Which SQL keyword is commonly used to start a Recursive CTE?

A SELECT

B WITH

C JOIN

D INSERT

WITH starts a CTE, including recursive ones.

Why must a Recursive CTE have a termination condition?

A To avoid infinite loops

B To speed up the query

C To join tables

D To create indexes

Without a termination condition, recursion would continue forever.

What kind of data is Recursive CTE especially good for?

A Flat lists

B Images

C Hierarchical or tree data

D Random numbers

Recursive CTEs are great for hierarchical data like org charts.

In PostgreSQL, which keyword must be added to WITH to make a CTE recursive?

A ITERATE

B LOOP

C REPEAT

D RECURSIVE

The RECURSIVE keyword tells PostgreSQL the CTE will call itself.

Explain how a Recursive CTE works step-by-step.

Think of climbing a ladder one step at a time until you reach the top.

Describe a real-world scenario where you would use a Recursive CTE.

Imagine finding all family members in a family tree.