LOOP, WHILE, FOR iterations in PostgreSQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a simple FOR loop that iterates from 1 to 5.

PostgreSQL

DO $$ BEGIN
  FOR i IN 1..[1] LOOP
    RAISE NOTICE 'Number: %', i;
  END LOOP;
END $$;

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A0

B10

C1

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Using 10 instead of 5 causes the loop to run too many times.

Using 0 or 1 as the upper limit will not loop five times.

The FOR loop runs from 1 to 5, so the upper limit should be 5.

2fill in blank

medium

Complete the code to create a WHILE loop that counts down from 3 to 1.

PostgreSQL

DO $$ DECLARE
  counter INTEGER := 3;
BEGIN
  WHILE counter > [1] LOOP
    RAISE NOTICE 'Count: %', counter;
    counter := counter - 1;
  END LOOP;
END $$;

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A4

B3

C0

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using 1 as the condition causes the loop to stop too early.

Using 3 or 4 causes the loop to never run or run incorrectly.

The loop continues while counter is greater than 0, counting down from 3 to 1.

3fill in blank

hard

Fix the error in the FOR loop that should iterate over an array of integers.

PostgreSQL

DO $$ DECLARE
  numbers INTEGER[] := ARRAY[2, 4, 6];
  num INTEGER;
BEGIN
  FOR num IN [1] LOOP
    RAISE NOTICE 'Value: %', num;
  END LOOP;
END $$;

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AUNNEST(numbers)

BSELECT * FROM numbers

C1..array_length(numbers, 1)

Dnumbers

Attempts:

3 left

💡 Hint

Common Mistakes

Using the array name directly does not work in FOR loops.

Using SELECT * FROM numbers is invalid because numbers is not a table.

Using 1..array_length(numbers, 1) loops over indexes, not values.

To loop over array elements in PostgreSQL, use UNNEST(array) in the FOR loop.

4fill in blank

hard

Fill both blanks to create a FOR loop that sums numbers from 1 to 4.

PostgreSQL

DO $$ DECLARE
  total INTEGER := 0;
BEGIN
  FOR i IN [1] LOOP
    total := total [2] i;
  END LOOP;
  RAISE NOTICE 'Sum: %', total;
END $$;

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A1..4

B+

C-

D5..10

Attempts:

3 left

💡 Hint

Common Mistakes

Using 5..10 loops over wrong numbers.

Using - subtracts instead of adds.

The loop runs from 1 to 4, adding each number to total using the + operator.

5fill in blank

hard

Fill all three blanks to create a WHILE loop that multiplies a number by 2 until it is greater than 20.

PostgreSQL

DO $$ DECLARE
  val INTEGER := [1];
BEGIN
  WHILE val [2] [3] LOOP
    RAISE NOTICE 'Value: %', val;
    val := val * 2;
  END LOOP;
END $$;

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A1

B<=

C20

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Starting val at 20 or higher causes no loop iterations.

Using > 20 as condition causes loop to never run.

Start val at 1, loop while val is less than or equal to 20, doubling val each time.