- A
Add the new columns using ALTER TABLE ADD COLUMN.
Adding new columns is necessary to include the two new nullable columns.
- B
Use the ALTER TABLE SET OPTIONS statement to change the column mode to NULLABLE.
Changing the column mode from REQUIRED to NULLABLE can be done using ALTER TABLE ALTER COLUMN (or SET OPTIONS as stated) without needing to export data.
- C
Update the IAM permissions on the table.
Why wrong: Updating IAM permissions is not related to schema evolution.
- D
Use CREATE OR REPLACE TABLE with the new schema and import data.
Why wrong: CREATE OR REPLACE TABLE with new schema and data import is a valid approach but is not required, as schema changes can be done directly.
- E
Export the table to Cloud Storage in Avro format.
Why wrong: Exporting data to Cloud Storage is part of a manual migration but is not necessary if using direct ALTER statements.
PDE Schema evolution Practice Question
This PDE practice question tests your understanding of maintaining and automating data workloads. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. A key principle to apply: schema evolution. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
You have a BigQuery table with a REQUIRED column that you now need to allow NULL values. You also need to add two new nullable columns. Which THREE steps are required to achieve this schema evolution? (Choose 3)
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Add the new columns using ALTER TABLE ADD COLUMN.
To achieve the schema evolution, you need to add the new nullable columns using ALTER TABLE ADD COLUMN (A) and change the existing REQUIRED column to NULLABLE using ALTER TABLE ALTER COLUMN DROP NOT NULL (the SET OPTIONS statement in option B approximates this). Exporting and recreating the table (D and E) are not required because BigQuery supports direct schema changes without data migration.
Key principle: Schema evolution
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Add the new columns using ALTER TABLE ADD COLUMN.
Why this is correct
Adding new columns is necessary to include the two new nullable columns.
Related concept
Schema evolution
- ✓
Use the ALTER TABLE SET OPTIONS statement to change the column mode to NULLABLE.
Why this is correct
Changing the column mode from REQUIRED to NULLABLE can be done using ALTER TABLE ALTER COLUMN (or SET OPTIONS as stated) without needing to export data.
Related concept
Schema evolution
- ✗
Update the IAM permissions on the table.
Why it's wrong here
Updating IAM permissions is not related to schema evolution.
- ✗
Use CREATE OR REPLACE TABLE with the new schema and import data.
Why it's wrong here
CREATE OR REPLACE TABLE with new schema and data import is a valid approach but is not required, as schema changes can be done directly.
- ✗
Export the table to Cloud Storage in Avro format.
Why it's wrong here
Exporting data to Cloud Storage is part of a manual migration but is not necessary if using direct ALTER statements.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Candidates may mistakenly believe that exporting and recreating the table is required to change a column from REQUIRED to NULLABLE, but BigQuery allows direct alteration.
Detailed technical explanation
How to think about this question
Treat this as a scenario question. Identify the problem, the constraint, and the best action. Then compare each option against those facts.
KKey Concepts to Remember
- Schema evolution
- ALTER TABLE ADD COLUMN
- ALTER TABLE ALTER COLUMN
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Schema evolution
Real-world example
How this comes up in practice
A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
What to study next
Got this wrong? Here's your next step.
Review schema evolution, then practise related PDE questions on the same topic to reinforce the concept.
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Maintaining and Automating Data Workloads — study guide chapter
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FAQ
Questions learners often ask
What does this PDE question test?
Maintaining and Automating Data Workloads — This question tests Maintaining and Automating Data Workloads — Schema evolution.
What is the correct answer to this question?
The correct answer is: Add the new columns using ALTER TABLE ADD COLUMN. — To achieve the schema evolution, you need to add the new nullable columns using ALTER TABLE ADD COLUMN (A) and change the existing REQUIRED column to NULLABLE using ALTER TABLE ALTER COLUMN DROP NOT NULL (the SET OPTIONS statement in option B approximates this). Exporting and recreating the table (D and E) are not required because BigQuery supports direct schema changes without data migration.
What should I do if I get this PDE question wrong?
Review schema evolution, then practise related PDE questions on the same topic to reinforce the concept.
What is the key concept behind this question?
Schema evolution
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Last reviewed: Jul 4, 2026
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