Vertica SQL queries to BigQuery
Translate Vertica SQL—analytic/window patterns, string/date idioms, and platform-specific query shapes—into BigQuery Standard SQL with validation gates that prevent semantic drift and scan-cost surprises.
- Input
- Vertica SQL / query migration logic
- Output
- BigQuery equivalent (validated)
- Common pitfalls
- Type coercion drift: Vertica implicit casts differ; BigQuery often needs explicit casts for stable outputs.
- NULL semantics in joins: join keys and filters change match behavior if null-safe rules aren’t explicit.
- Window ordering ambiguity: ROW_NUMBER/RANK without stable tie-breakers causes nondeterministic drift.
Why this breaks
Vertica SQL estates frequently rely on analytic-window logic, implicit casting behavior, and execution assumptions shaped by projections and segmentation. In BigQuery, queries may compile after translation, but drift appears when implicit type/NULL behavior differs and when ordering in window/top-N logic isn’t fully deterministic. Costs also spike when Vertica-era shapes don’t translate into BigQuery pruning-friendly filters.
Common symptoms after cutover:
- KPI drift from window logic and top-N selections with incomplete ordering
- Dedupe behavior changes under retries because tie-breakers were implicit
- Date/time logic shifts due to timezone assumptions and DATE vs TIMESTAMP intent
- String/regex edge cases differ across dialects
- Costs spike because filters and joins aren’t pruning-friendly in BigQuery
SQL migration must preserve both meaning and a BigQuery-native execution posture.
How conversion works
- Inventory & prioritize the Vertica SQL corpus (reports, views, ETL SQL, BI extracts). Rank by business impact and risk patterns (windows, time, casts, top-N).
- Normalize Vertica dialect: identifiers, CTE shapes, and common function idioms to reduce noise.
- Rewrite with rule-anchored mappings: Vertica functions → BigQuery equivalents, explicit cast strategy, and deterministic ordering for windowed filters.
- Pruning-first refactors: translate access-path assumptions into BigQuery partition filters and clustering-aligned predicates.
- Validate with gates: compilation, catalog/type alignment, golden-query parity, and edge-cohort diffs.
- Performance-safe rewrites: adjust joins, aggregation shapes, and recommend materializations for the heaviest BI queries.
Supported constructs
Representative Vertica SQL constructs we commonly convert to BigQuery Standard SQL (exact coverage depends on your estate).
| Source | Target | Notes |
|---|---|---|
| Vertica analytic/window patterns | BigQuery window functions + QUALIFY | Deterministic ordering and tie-breakers enforced. |
| ROW_NUMBER-based dedupe patterns | Windowed dedupe with explicit tie-breakers | Prevents nondeterministic drift under retries. |
| DATE/TIMESTAMP arithmetic | BigQuery date/time functions | Timezone intent normalized explicitly. |
| NULL/type coercion idioms | Explicit CAST + SAFE_CAST patterns | Prevents branch type drift and join-key mismatch. |
| String/regex functions | BigQuery string/regex equivalents | Edge-case behavior validated via golden cohorts. |
| Access-path assumptions (projection-driven) | Pruning-first SQL + partitioning/clustering alignment | Replace projection thinking with scan-cost governance. |
How workload changes
| Topic | Vertica | BigQuery |
|---|---|---|
| Execution assumptions | Projection/segmentation-driven performance expectations | Pruning-first filters + partitioning/clustering alignment |
| Typing behavior | Implicit casts common | Explicit casts recommended for stable outputs |
| Time semantics | Timezone assumptions often implicit | Explicit DATE vs TIMESTAMP + timezone conversions |
Examples
Representative Vertica → BigQuery rewrites for windowed dedupe and date/time functions. Adjust identifiers and types to your schema.
-- Vertica: latest row per key
SELECT *
FROM events
QUALIFY ROW_NUMBER() OVER (
PARTITION BY business_key
ORDER BY event_ts DESC
) = 1;Common pitfalls
- Type coercion drift: Vertica implicit casts differ; BigQuery often needs explicit casts for stable outputs.
- NULL semantics in joins: join keys and filters change match behavior if null-safe rules aren’t explicit.
- Window ordering ambiguity: ROW_NUMBER/RANK without stable tie-breakers causes nondeterministic drift.
- Top-N without deterministic ORDER BY: paging results differ even when totals look right.
- Timezone assumptions: boundary-day reporting drifts unless standardized.
- Pruning defeated: filters wrap partition columns or cast in WHERE, causing scan bytes explosion.
- Over-trusting “it runs”: compilation success is not parity; validate with golden outputs and edge cohorts.
Validation approach
- Compilation gates: converted queries compile and execute in BigQuery reliably under representative parameters.
- Catalog/type checks: referenced objects exist; implicit casts surfaced and made explicit.
- Golden-query parity: business-critical queries/dashboards match outputs or agreed tolerances.
- KPI aggregates: compare aggregates by key dimensions and cohorts.
- Edge-cohort diffs: validate ties, null-heavy segments, boundary dates, and timezone transitions.
- Pruning/performance baseline: capture runtime/bytes scanned/slot time for top queries; set regression thresholds.
Migration steps
- 01
Collect and prioritize the query estate
Export BI SQL, view definitions, ETL SQL, and app queries. Rank by business impact, frequency, and risk patterns (windows, time logic, implicit casts, top-N).
- 02
Define semantic and pruning contracts
Make tie-breakers, NULL handling, casting strategy, and timezone intent explicit. Define pruning expectations and scan-byte thresholds for the top queries.
- 03
Convert with rule-anchored mappings
Apply deterministic rewrites for Vertica constructs and flag ambiguous intent with review markers (implicit casts, ordering ambiguity, time semantics).
- 04
Validate with golden queries and edge cohorts
Compile and run in BigQuery, compare KPI aggregates, and run targeted diffs on edge cohorts (ties, null-heavy segments, boundary dates).
- 05
Tune top queries for BigQuery
Align partitioning/clustering to access paths, enforce pruning-first filters, and recommend materializations for the most expensive BI workloads.
We inventory your SQL estate, convert a representative slice, and deliver parity evidence on golden queries—plus pruning baselines so BigQuery spend stays predictable.
Get a conversion plan, review markers, and validation artifacts so query cutover is gated by evidence and rollback-ready criteria—without scan-cost surprises.