Moderate SQL Question 94 of 226

GROUP BY versus SELECT DISTINCT: how do you choose?

Java Specialist · Speak this in 60–90 seconds · Faridabad & Delhi NCR

Without indexScan every row

With indexJump to keys

CostWrites slower

DISTINCT removes duplicate result rows.

Why interviewers care about SQL:

They want a clean

contrast on SQL, not two memorised paragraphs.

Say what changes for

the developer, then one case where picking wrong hurts.

Stay structured

Name the idea, why it exists, then one short example.

Close cleanly

End with when you use it and one common pitfall.

Before you speak the answer, walk the interviewer through these steps:

1
Define it
DISTINCT removes duplicate result rows.
2
GROUP BY clusters rows
to compute aggregates such as COUNT and SUM.
3
If you are not
aggregating, DISTINCT is clearer
4
if you need totals
per customer, you must GROUP BY the non-aggregated columns.
5
Common mistake
What juniors usually get wrong.
6
Close
When you pick this over the alternative.

Here's a short line you can speak, broken into clear beats:

Say this line

“GROUP BY clusters rows to compute aggregates such as COUNT and SUM.”

Break into beats

GROUPBYclustersrowstocompute

Speaking order

2987408337471632900

Note: Adapt this scaffold to your own project — keep it under 60–90 seconds.

DISTINCT removes duplicate result rows. GROUP BY clusters rows to compute aggregates such as COUNT and SUM.