PDE Maintaining and Automating Data Workloads Practice Question
Which BigQuery feature allows you to estimate the cost of a query before running it, by returning the number of bytes that would be processed?
⚠ Common exam trap
The trap is confusing the dry run flag with other features like EXPLAIN or INFORMATION_SCHEMA, which serve different purposes.
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
✓
--dry_run flag
The --dry_run flag in BigQuery allows you to validate a query and estimate the number of bytes it will process without actually running it, thus providing a cost estimate. This is a standard feature in the bq command-line tool and the BigQuery API. It returns the total bytes processed, which can be used to calculate the cost based on current pricing.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
EXPLAIN statement
Why it's wrong here
BigQuery has no EXPLAIN statement; that construct belongs to systems such as PostgreSQL and MySQL for showing query plans. It is tempting because EXPLAIN sounds like a pre-execution inspection tool, but BigQuery instead offers dry runs, which return the total bytes processed without running the query.
- ✗
INFORMATION_SCHEMA.JOBS
Why it's wrong here
INFORMATION_SCHEMA.JOBS lists historical job metadata after execution, so it reports bytes billed for completed queries rather than estimating a new one. It is tempting because it exposes bytes processed, but that is retrospective auditing; a dry run returns the estimate before the query runs.
- ✓
--dry_run flag
Why this is correct
The `--dry_run` flag validates a query and returns the bytes it would process without executing it, so no compute charges are incurred. This directly satisfies the stem's requirement to estimate cost before running, since BigQuery on-demand pricing is calculated from bytes processed.
- ✗
Slot estimator
Why it's wrong here
Slot estimator concerns reserving or forecasting compute capacity, not query byte volume. It is tempting because slots relate to BigQuery pricing and performance, but cost estimation before execution comes from a dry run, which returns the bytes the query would process.
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Last reviewed September 2026 · checked against the official Google Cloud exam blueprint
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