Interview Question: How to Retrieve Unique Values without Using DISTINCT keyword

Question: List unique jobs (from emp table) without using DISTINCT keyword

Question Level: Beginner+

We picked 5 different methods (workarounds) to show in this post. It is possible to produce at least 15 if you read some other posts in this blog.

Method/Workaround #1: Use GROUP BY (Level: Beginner)

SELECT job
FROM emp
GROUP BY job

Method/Workaround #2: Use Analytical functions with a subquery (Level: Intermediate)

SELECT job
FROM(SELECT job, ROW_NUMBER()OVER(PARTITION BY job ORDER BY 1) rn
     FROM emp) 
WHERE rn=1

Method/Workaround #3: Use correlated subquery (Level: Intermediate)

SELECT job
FROM emp a
WHERE empno=(SELECT MAX(empno) 
             FROM emp
             WHERE job=a.job)

Method/Workaround #4: Use left join with IS NULL filter (Level: Advanced)

SELECT a.job
FROM emp a LEFT JOIN emp b ON a.job=b.job AND a.empno<b.empno
WHERE b.empno IS NULL

Method/Workaround #5: Use NOT EXIST (Level: Intermediate)

SELECT job
FROM emp a
WHERE NOT EXISTS(SELECT 1
                 FROM emp b
                 WHERE a.job=b.job 
                   AND b.empno>a.empno)

For more tricks and cool techniques check my book “Oracle SQL Tricks and Workarounds” for instructions.

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