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Fixes on getting started BQ article #23

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41 changes: 9 additions & 32 deletions src/content/articles/getting-started-bigquery.md
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Expand Up @@ -44,38 +44,28 @@ BigQuery's `bq` command-line tool is now available and queries against `measurem

If you need to query from an application using a service account (`@developer.gserviceaccount.com`), email [support@measurementlab.net](mailto:support@measurementlab.net) so M-Lab can add it to M-Lab Discuss manually. Ensure the account has the **BigQuery User**, **BigQuery Job User**, and **BigQuery Data Viewer** IAM roles on the `measurement-lab` project.

## Key Datasets

| Dataset | Description |
|---------|-------------|
| `ndt` | NDT speed tests — use `ndt7_union` for general analysis |
| `ndt_raw` | Raw NDT archives including traceroute and TCP info |
| `msak` / `msak_raw` | Multi-stream throughput measurements |
| `wehe_raw` | App-specific traffic differentiation tests |

For most use cases, start with `measurement-lab.ndt.ndt7_union`.

## Your First Query

Average download speed by country for the last 30 days:
For speed test results, you can start with the `measurement-lab.ndt.ndt7_union` table.
For example, for the average download speed by country for the last 30 days:

<!-- sqltest -->
```sql
-- Average download speed by country for the last 30 days
-- Median download speed by country for a day
SELECT
client.Geo.CountryCode AS country,
ROUND(AVG(a.MeanThroughputMbps), 2) AS avg_download_mbps,
ROUND(APPROX_QUANTILES(a.MeanThroughputMbps, 2)[OFFSET(1)], 2) AS median_download_mbps,
COUNT(*) AS test_count
FROM `measurement-lab.ndt.ndt7_union`
WHERE date >= DATE_SUB(CURRENT_DATE(), INTERVAL 30 DAY)
WHERE date = '2024-06-01'
AND a.MeanThroughputMbps > 0
AND a.MeanThroughputMbps < 10000 -- exclude outliers
GROUP BY country
ORDER BY avg_download_mbps DESC
ORDER BY median_download_mbps DESC
LIMIT 20
```

## Understanding the Schema
### Understanding the Schema

NDT7 results have a nested structure. The key top-level fields are:

Expand Down Expand Up @@ -103,20 +93,9 @@ server.Site — M-Lab site ID (e.g., "lga01")
server.Metro — metro area (e.g., "lga" for New York)
```

## Unified Views vs. Raw Tables

M-Lab provides both raw tables and cleaned **unified views**:

- `measurement-lab.ndt.ndt7_union` — **recommended** for most analysis; quality-filtered, includes M-Lab-managed and Host-Managed server data
- `measurement-lab.ndt.ndt7` — M-Lab-managed servers only
- `measurement-lab.ndt.ndt7_dynamic` — Host-Managed servers only
- `measurement-lab.ndt_raw.*` — unfiltered 1-to-1 archives; use only if you need test failures or custom quality logic

The unified views exclude tests shorter than 9 seconds, tests with less than 8 KB transferred, and M-Lab's own monitoring traffic.

## Query Costs and Partition Pruning

The NDT7 table is large (~5 TB/month of new data). **Always** filter by `DATE(a.TestTime)` to use BigQuery's partition pruning:
The NDT7 table is large (~0.5 TB/day of new data). **Always** filter by `DATE(a.TestTime)` to use BigQuery's partition pruning:

```sql
-- Efficient: uses partition pruning
Expand All @@ -126,7 +105,7 @@ WHERE DATE(a.TestTime) = '2024-06-01'
WHERE a.TestTime > '2024-06-01'
```

Use the **preview** feature in the BigQuery UI to inspect data before running queries, and add `LIMIT` clauses during development.
Use the **preview** feature in the BigQuery UI to inspect data before running queries. The daily query limit per user per day is currently set to 10TiB.

## Exporting Data

Expand All @@ -151,8 +130,6 @@ AS (
## Further Reading

- [M-Lab BigQuery Schema](https://www.measurementlab.net/data/docs/bq/schema) — full schema documentation
- [Google BigQuery documentation](https://cloud.google.com/bigquery/what-is-bigquery)
- [Querying date-partitioned tables](https://cloud.google.com/bigquery/docs/querying-partitioned-tables)
- [NDT (Network Diagnostic Tool)](../test-ndt) — the primary dataset
- [Analyzing M-Lab Data: A Researcher's Guide](../research-guide) — ISP comparison patterns and advanced queries

Expand Down
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