Objective

Write a SQL query to identify candidates who have all three required skills: Python, Tableau, and PostgreSQL.

Table Schema:

• candidates

Task Requirements:

• Identify candidates who have Python, Tableau, and PostgreSQL skills
• Return only the candidate IDs of qualified candidates
• Sort results in ascending order by candidate_id
  
  

Output columns: candidate_id

SELECT 
    candidate_id
FROM candidates
WHERE skill IN ('Python', 'Tableau', 'PostgreSQL')
GROUP BY candidate_id
HAVING COUNT(DISTINCT skill) = 3
ORDER BY candidate_id ASC;

Explanation

Step 1: Filter for Target Skills

The WHERE clause narrows the dataset to only the three relevant skills, eliminating irrelevant rows before aggregation.

WHERE skill IN ('Python', 'Tableau', 'PostgreSQL')

Step 2: Group by Candidate

Group by candidate_id to aggregate each candidate's skills together.

GROUP BY candidate_id

Step 3: Require All Three Skills

Use HAVING COUNT(DISTINCT skill) = 3 to keep only candidates who have all three distinct target skills. DISTINCT prevents double-counting if a skill appears multiple times.

HAVING COUNT(DISTINCT skill) = 3

Step 4: Sort Results

Order by candidate_id ascending for a clean, organized output.

ORDER BY candidate_id ASC