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Write code to read data from Delta Lake in S3 and perform upsert based on primary key

Spark/Big Datamedium0.6 min readPremium
Frequency
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Asked at 1 company
Category
452
questions in Spark/Big Data
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88E|81M|283H
in this category
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1,863
across 7 categories
Asked at these companies
Walmart
Key Concepts Tested
partitionspark
Expert AnswerPremium
112 wordsInterview-ready
**Why It Matters (Architectural Logic)**: MERGE enables CDC and incremental loads—update existing, insert new. Partition pruning on merge key is critical for performance. Delta Lake MERGE supports upsert by primary key. Read existing: `from delta.tables import DeltaTable; delta = DeltaTable.forPath(spark, "s3://bucket/table")`. Merge: `delta.alias("t").merge(new_df.alias("s"), "t.id = s.id").whenMatchedUpdate(set={"col": "s.col"}).whenNotMatchedInsertAll().execute()`....
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