Recursive CTE for series generation in SQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start the recursive CTE with the initial value 1.

SQL

WITH RECURSIVE numbers AS (SELECT [1] AS n

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A1

B0

Cn

DNULL

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 instead of 1 as the starting value.

Using a column name instead of a constant.

Leaving the value NULL.

The recursive CTE must start with the initial value 1, so we select 1 as n.

2fill in blank

medium

Complete the recursive part to add 1 to the previous number.

SQL

UNION ALL SELECT n [1] 1 FROM numbers WHERE n < 5)

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A*

B-

C+

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using subtraction or multiplication instead of addition.

Forgetting to limit the recursion with a WHERE clause.

The recursive step adds 1 to the previous number to generate the next number in the series.

3fill in blank

hard

Fix the error in the final SELECT to get all numbers from the CTE.

SQL

SELECT [1] FROM numbers;

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A*

Bn

Cnumbers

Dcount

Attempts:

3 left

💡 Hint

Common Mistakes

Selecting '*' returns all columns but here only 'n' is defined.

Selecting the CTE name instead of the column.

Using an undefined column like 'count'.

The CTE defines a column named 'n', so we select 'n' to get the series values.

4fill in blank

hard

Fill both blanks to generate numbers from 10 to 15 using a recursive CTE.

SQL

WITH RECURSIVE seq AS (SELECT [1] AS num UNION ALL SELECT num [2] 1 FROM seq WHERE num < 15) SELECT num FROM seq;

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A10

B+

C-

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Starting at the wrong number.

Using subtraction instead of addition.

Not incrementing the number.

The series starts at 10 and increments by 1 until 15.

5fill in blank

hard

Fill all three blanks to create a recursive CTE that generates even numbers from 2 to 10.

SQL

WITH RECURSIVE evens AS (SELECT [1] AS val UNION ALL SELECT val [2] [3] FROM evens WHERE val < 10) SELECT val FROM evens;

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A2

B+

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Starting at 1 instead of 2.

Adding 1 instead of 2.

Using multiplication or subtraction.

The series starts at 2 and adds 2 each time to get even numbers up to 10.