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Databricks Certified Data Engineer Professional Exam - Topic 2 Question 34 Discussion

A data engineer is configuring a pipeline that will potentially see late-arriving, duplicate records.In addition to de-duplicating records within the batch, which of the following approaches allows the data engineer to deduplicate data against previously processed records as it is inserted into a Delta table?
C) Perform an insert-only merge with a matching condition on a unique key.
A) Set the configuration delta.deduplicate = true.
B) VACUUM the Delta table after each batch completes.
D) Perform a full outer join on a unique key and overwrite existing data.
E) Rely on Delta Lake schema enforcement to prevent duplicate records.

Databricks Certified Data Engineer Professional Exam - Topic 2 Question 34 Discussion

Actual exam question for Databricks's Databricks Certified Data Engineer Professional exam
Question #: 34
Topic #: 2
[All Databricks Certified Data Engineer Professional Questions]

A data engineer is configuring a pipeline that will potentially see late-arriving, duplicate records.

In addition to de-duplicating records within the batch, which of the following approaches allows the data engineer to deduplicate data against previously processed records as it is inserted into a Delta table?

Show Suggested Answer Hide Answer
Suggested Answer: C

To deduplicate data against previously processed records as it is inserted into a Delta table, you can use the merge operation with an insert-only clause. This allows you to insert new records that do not match any existing records based on a unique key, while ignoring duplicate records that match existing records. For example, you can use the following syntax:

MERGE INTO target_table USING source_table ON target_table.unique_key = source_table.unique_key WHEN NOT MATCHED THEN INSERT *

This will insert only the records from the source table that have a unique key that is not present in the target table, and skip the records that have a matching key. This way, you can avoid inserting duplicate records into the Delta table.


https://docs.databricks.com/delta/delta-update.html#upsert-into-a-table-using-merge

https://docs.databricks.com/delta/delta-update.html#insert-only-merge

by Georgiann at May 04, 2025, 10:52 PM

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Dottie
7 months ago
VACUUM is more about cleanup, not deduplication.
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Lajuana
7 months ago
Wait, does E really prevent duplicates?
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Denise
7 months ago
I disagree, D could work too.
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Yolando
7 months ago
A doesn't actually do what we need here.
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Glory
7 months ago
C is the best option for deduplication.
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Yuki
8 months ago
I thought schema enforcement was more about data types and structure, not really about duplicates, so E doesn't seem right to me.
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Francesco
8 months ago
I practiced a similar question where we had to manage late-arriving data, and I think using a unique key in a merge could help, so C sounds plausible.
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Ilene
8 months ago
I'm not entirely sure, but I feel like VACUUMing the Delta table is more about cleanup than deduplication, so B seems off.
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Phung
8 months ago
I remember something about using merge operations to handle duplicates, so I think C might be the right choice.
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Ligia
9 months ago
Hmm, I'm not sure about this. The options all seem plausible, and I'm not sure I fully understand the nuances of how Delta Lake handles deduplication. I think I'll need to review the Delta Lake documentation again before deciding on an answer.
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Bernadine
9 months ago
This seems straightforward to me. Option C is clearly the way to go - the insert-only merge will ensure that any duplicate records are skipped, while still allowing new unique records to be added to the Delta table. I feel pretty confident about this one.
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Kristal
9 months ago
I'm a bit confused by the wording here. What exactly does "deduplicate data against previously processed records" mean? Is that different from just deduplicating within the batch? I'll need to re-read this a few times to make sure I'm understanding it correctly.
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Tashia
9 months ago
Okay, I think I've got this. The key is to find a way to deduplicate the data as it's being inserted into the Delta table, rather than just within the batch. I'm leaning towards option C - the insert-only merge with a unique key condition.
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Royal
9 months ago
Hmm, this looks like a tricky one. I'll need to think through the different options carefully to make sure I understand the implications of each approach.
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Justine
1 year ago
You know, Option A, 'Set the configuration delta.deduplicate = true' sounds a bit too good to be true. I bet there's more to it than just flipping a switch.
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Sylvia
1 year ago
Ha! Option B, 'VACUUM the Delta table'? That's like trying to sweep dust under the rug. Let's be real, we need a proper deduplication strategy here.
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Fallon
12 months ago
That could work, as long as we handle conflicts properly.
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Tandra
12 months ago
Option D) Perform a full outer join on a unique key and overwrite existing data.
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Denise
1 year ago
But what if we need to update existing records as well?
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Natalie
1 year ago
Option C) Perform an insert-only merge with a matching condition on a unique key.
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Maryann
1 year ago
Hmm, I'm not sure about Option E. Relying on Delta Lake schema enforcement alone seems a bit risky for deduplicating data. I'd go with Option C or D.
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Cristy
1 year ago
I think D) Perform a full outer join on a unique key and overwrite existing data could also be a valid approach.
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Solange
1 year ago
But wouldn't setting the configuration delta.deduplicate = true also help in deduplicating data?
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Paris
1 year ago
I think Option D is the way to go. A full outer join on a unique key and overwriting the existing data is a robust way to handle late-arriving, duplicate records.
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Ellsworth
1 year ago
Performing a full outer join on a unique key can help prevent any issues with duplicate data in the Delta table.
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Kenneth
1 year ago
Option D is a good choice. It's important to handle late-arriving, duplicate records effectively.
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Macy
1 year ago
Option C looks like the best approach to me. Performing an insert-only merge with a unique key condition will allow the data engineer to deduplicate the data as it's inserted into the Delta table.
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Elly
1 year ago
User 3: It definitely makes sense to prevent duplicate records by merging based on a unique key.
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Dominga
1 year ago
User 2: Yeah, using a unique key condition in an insert-only merge is a smart approach.
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Willodean
1 year ago
User 1: I agree, option C seems like the most efficient way to deduplicate the data.
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Lonny
1 year ago
I disagree, I believe the correct answer is E) Rely on Delta Lake schema enforcement to prevent duplicate records.
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Solange
1 year ago
I think the answer is C) Perform an insert-only merge with a matching condition on a unique key.
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