IF-ELSIF-ELSE control flow in PostgreSQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Output of IF-ELSIF-ELSE in a PL/pgSQL function

Consider the following PostgreSQL function. What will be the output when calling check_number(15)?

PostgreSQL

CREATE OR REPLACE FUNCTION check_number(num INTEGER) RETURNS TEXT AS $$
BEGIN
  IF num < 10 THEN
    RETURN 'Less than 10';
  ELSIF num < 20 THEN
    RETURN 'Between 10 and 19';
  ELSE
    RETURN '20 or more';
  END IF;
END;
$$ LANGUAGE plpgsql;

A 'Between 10 and 19'

B 'Less than 10'

C '20 or more'

D NULL

💡 Hint

Think about which condition matches the input number 15.

The function checks if the number is less than 10, then between 10 and 19, else 20 or more. Since 15 is between 10 and 19, it returns 'Between 10 and 19'.

📝 Syntax

intermediate

Identify the syntax error in IF-ELSIF-ELSE block

Which option contains a syntax error in the IF-ELSIF-ELSE block in PostgreSQL PL/pgSQL?

PostgreSQL

BEGIN
  IF x = 1 THEN
    RAISE NOTICE 'One';
  ELSEIF x = 2 THEN
    RAISE NOTICE 'Two';
  ELSE
    RAISE NOTICE 'Other';
  END IF;
END;

A Remove ELSE block

B Replace END IF with END

C Add semicolon after THEN

D Replace ELSEIF with ELSIF

💡 Hint

Check the correct keyword spelling for else-if in PL/pgSQL.

In PL/pgSQL, the correct keyword is ELSIF, not ELSEIF. Using ELSEIF causes a syntax error.

❓ query_result

advanced

Result of nested IF-ELSIF-ELSE in a function

What will be the output of evaluate_score(75) given this function?

PostgreSQL

CREATE OR REPLACE FUNCTION evaluate_score(score INTEGER) RETURNS TEXT AS $$
BEGIN
  IF score >= 90 THEN
    RETURN 'Excellent';
  ELSIF score >= 70 THEN
    IF score >= 80 THEN
      RETURN 'Very Good';
    ELSE
      RETURN 'Good';
    END IF;
  ELSE
    RETURN 'Needs Improvement';
  END IF;
END;
$$ LANGUAGE plpgsql;

A 'Good'

B 'Very Good'

C 'Excellent'

D 'Needs Improvement'

💡 Hint

Check the nested IF conditions carefully for score 75.

75 is >= 70 but less than 80, so the inner IF returns 'Good'.

🔧 Debug

advanced

Find the logical error in IF-ELSIF-ELSE

This function is intended to classify ages but returns incorrect results for age 18. What is the logical error?

PostgreSQL

CREATE OR REPLACE FUNCTION classify_age(age INTEGER) RETURNS TEXT AS $$
BEGIN
  IF age < 13 THEN
    RETURN 'Child';
  ELSIF age > 13 AND age < 18 THEN
    RETURN 'Teenager';
  ELSE
    RETURN 'Adult';
  END IF;
END;
$$ LANGUAGE plpgsql;

A Should use OR instead of AND in ELSIF

B Missing ELSEIF for age = 18

C The condition excludes age 13 and 18 from 'Teenager' category

D RETURN statements are misplaced

💡 Hint

Check the conditions carefully for boundary ages 13 and 18.

The ELSIF condition uses > 13 and < 18, so age 13 and 18 do not match 'Teenager'. Age 13 is classified as 'Adult' incorrectly.

❓ optimization

expert

Optimize IF-ELSIF-ELSE for performance

Which option optimizes this IF-ELSIF-ELSE block for better performance when checking multiple conditions on a variable val?

PostgreSQL

IF val = 1 THEN
  RETURN 'One';
ELSIF val = 2 THEN
  RETURN 'Two';
ELSIF val = 3 THEN
  RETURN 'Three';
ELSE
  RETURN 'Other';
END IF;

A Use nested IF statements for each condition

B Use CASE statement instead of IF-ELSIF-ELSE

C Replace ELSE with another ELSIF for val = 4

D Use multiple IF statements without ELSIF

💡 Hint

Consider which control structure is more efficient and readable for multiple discrete values.

CASE statements are optimized for multiple discrete value checks and improve readability and performance over multiple IF-ELSIF-ELSE blocks.