BigQuery Expert Engineer Skill

This skill provides a comprehensive guide for BigQuery development.

1. bq Command Line Tool Basics

1.1. Query Execution

# Execute query with Standard SQL
bq query --use_legacy_sql=false 'SELECT * FROM `project.dataset.table` LIMIT 10'

# Output results in CSV format
bq query --use_legacy_sql=false --format=csv 'SELECT * FROM `project.dataset.table`'

# Dry run (cost estimation)
bq query --use_legacy_sql=false --dry_run 'SELECT * FROM `project.dataset.table`'

# Save results to table
bq query --use_legacy_sql=false --destination_table=project:dataset.result_table 'SELECT * FROM `project.dataset.table`'

1.2. Table Operations

# List tables
bq ls project:dataset

# Check table schema
bq show --schema --format=prettyjson project:dataset.table

# Create table (from schema file)
bq mk --table project:dataset.table schema.json

# Create partitioned table
bq mk --table --time_partitioning_field=created_at project:dataset.table schema.json

# Create clustered table
bq mk --table --clustering_fields=user_id,category project:dataset.table schema.json

# Delete table
bq rm -t project:dataset.table

1.3. Data Load/Export

# Load from CSV
bq load --source_format=CSV project:dataset.table gs://bucket/data.csv schema.json

# Load from JSON
bq load --source_format=NEWLINE_DELIMITED_JSON project:dataset.table gs://bucket/data.json

# Load from Parquet (auto-detect schema)
bq load --source_format=PARQUET --autodetect project:dataset.table gs://bucket/data.parquet

# Export to Cloud Storage
bq extract --destination_format=CSV project:dataset.table gs://bucket/export/*.csv

2. GoogleSQL Basic Syntax

2.1. SELECT Statement

-- Basic SELECT
SELECT
  column1,
  column2,
  COUNT(*) AS count
FROM
  `project.dataset.table`
WHERE
  date >= '2024-01-01'
GROUP BY
  column1, column2
HAVING
  COUNT(*) > 10
ORDER BY
  count DESC
LIMIT 100

2.2. Common Functions

-- String functions
CONCAT(str1, str2)
LOWER(str), UPPER(str)
TRIM(str), LTRIM(str), RTRIM(str)
SUBSTR(str, start, length)
REGEXP_CONTAINS(str, r'pattern')
REGEXP_EXTRACT(str, r'pattern')
SPLIT(str, delimiter)

-- Date/time functions
CURRENT_DATE(), CURRENT_TIMESTAMP()
DATE(timestamp), TIMESTAMP(date)
DATE_ADD(date, INTERVAL 1 DAY)
DATE_DIFF(date1, date2, DAY)
FORMAT_DATE('%Y-%m-%d', date)
PARSE_DATE('%Y%m%d', str)
EXTRACT(YEAR FROM date)

-- Aggregate functions
COUNT(*), COUNT(DISTINCT column)
SUM(column), AVG(column)
MIN(column), MAX(column)
ARRAY_AGG(column)
STRING_AGG(column, ',')

-- Window functions
ROW_NUMBER() OVER (PARTITION BY col ORDER BY col2)
RANK() OVER (ORDER BY col DESC)
LAG(col, 1) OVER (ORDER BY date)
LEAD(col, 1) OVER (ORDER BY date)
SUM(col) OVER (PARTITION BY category)

2.3. JOIN Syntax

-- INNER JOIN
SELECT a.*, b.column
FROM `project.dataset.table_a` AS a
INNER JOIN `project.dataset.table_b` AS b
  ON a.id = b.id

-- LEFT JOIN
SELECT a.*, b.column
FROM `project.dataset.table_a` AS a
LEFT JOIN `project.dataset.table_b` AS b
  ON a.id = b.id

-- CROSS JOIN (commonly used for array expansion)
SELECT *
FROM `project.dataset.table`,
UNNEST(array_column) AS element

2.4. CTE (Common Table Expressions)

WITH
  base_data AS (
    SELECT *
    FROM `project.dataset.table`
    WHERE date >= '2024-01-01'
  ),
  aggregated AS (
    SELECT
      category,
      COUNT(*) AS count
    FROM base_data
    GROUP BY category
  )
SELECT *
FROM aggregated
ORDER BY count DESC

3. Table Design

3.1. Partitioning

Divide data by date to reduce query scan volume.

-- Create date-partitioned table
CREATE TABLE `project.dataset.partitioned_table`
PARTITION BY DATE(created_at)
AS SELECT * FROM `project.dataset.source_table`;

-- Integer partitioning
CREATE TABLE `project.dataset.int_partitioned`
PARTITION BY RANGE_BUCKET(user_id, GENERATE_ARRAY(0, 1000000, 10000))
AS SELECT * FROM source;

-- Require partition filter
CREATE TABLE `project.dataset.table`
PARTITION BY DATE(created_at)
OPTIONS (
  require_partition_filter = TRUE
);

3.2. Clustering

Sort and group data by specified columns.

-- Clustering table
CREATE TABLE `project.dataset.clustered_table`
PARTITION BY DATE(created_at)
CLUSTER BY user_id, category
AS SELECT * FROM source;

3.3. Best Practices

• Combine partitioning and clustering
• Choose columns frequently filtered in queries
• Maximum 4 clustering columns
• Prioritize high-cardinality columns

4. Performance Optimization

4.1. Query Optimization

-- Avoid SELECT *
-- Bad
SELECT * FROM table;
-- Good
SELECT column1, column2 FROM table;

-- Leverage partition pruning
-- Bad (function applied to partition column)
WHERE DATE(created_at) = '2024-01-01'
-- Good
WHERE created_at >= '2024-01-01' AND created_at < '2024-01-02'

-- Use APPROX_ functions for estimates (faster)
SELECT APPROX_COUNT_DISTINCT(user_id) FROM table;

4.2. JOIN Optimization

-- Put smaller table on right side (broadcast JOIN)
SELECT *
FROM large_table
JOIN small_table ON large_table.id = small_table.id;

-- JOIN only needed columns
WITH filtered AS (
  SELECT id, needed_column FROM large_table WHERE condition
)
SELECT * FROM filtered JOIN other_table ON ...

4.3. Check Slot Usage

-- Check job statistics
SELECT
  job_id,
  total_bytes_processed,
  total_slot_ms,
  TIMESTAMP_DIFF(end_time, start_time, SECOND) AS duration_sec
FROM `region-us`.INFORMATION_SCHEMA.JOBS
WHERE creation_time > TIMESTAMP_SUB(CURRENT_TIMESTAMP(), INTERVAL 1 DAY)
ORDER BY total_slot_ms DESC
LIMIT 10;

5. Cost Management

5.1. Pricing Model

• On-demand: Based on scanned data ($5/TB)
• Flat-rate (Editions): Based on reserved slots
• Storage: Active $0.02/GB, Long-term $0.01/GB

5.2. Cost Reduction Best Practices

1. Avoid SELECT *
2. Always use partition filters
3. Check cost with dry run before queries
4. Optimize repeated queries with materialized views
5. Speed up dashboard queries with BI Engine

5.3. Custom Quota Settings

-- Set query byte limit per project
-- Configure in Cloud Console or gcloud

6. Data Governance

6.1. IAM Roles

• roles/bigquery.admin

  : Full permissions

• roles/bigquery.dataEditor

  : Read/write data

• roles/bigquery.dataViewer

  : Read-only data

• roles/bigquery.jobUser

  : Execute jobs

• roles/bigquery.user

  : List datasets, execute jobs

6.2. Column-level Security

-- Apply policy tag
ALTER TABLE `project.dataset.table`
ALTER COLUMN sensitive_column
SET OPTIONS (policy_tags = ['projects/project/locations/us/taxonomies/123/policyTags/456']);

6.3. Row-level Security

-- Create row access policy
CREATE ROW ACCESS POLICY region_filter
ON `project.dataset.table`
GRANT TO ('user:analyst@example.com')
FILTER USING (region = 'APAC');

7. BigQuery ML

7.1. Model Creation

-- Linear regression model
CREATE OR REPLACE MODEL `project.dataset.model`
OPTIONS (
  model_type = 'LINEAR_REG',
  input_label_cols = ['target']
) AS
SELECT feature1, feature2, target
FROM `project.dataset.training_data`;

-- Logistic regression model
CREATE OR REPLACE MODEL `project.dataset.classifier`
OPTIONS (
  model_type = 'LOGISTIC_REG',
  input_label_cols = ['label']
) AS
SELECT * FROM training_data;

7.2. Model Evaluation and Prediction

-- Model evaluation
SELECT * FROM ML.EVALUATE(MODEL `project.dataset.model`);

-- Prediction
SELECT *
FROM ML.PREDICT(
  MODEL `project.dataset.model`,
  (SELECT * FROM `project.dataset.new_data`)
);

8. External Data Sources

8.1. External Tables

-- Reference Cloud Storage CSV as external table
CREATE EXTERNAL TABLE `project.dataset.external_table`
OPTIONS (
  format = 'CSV',
  uris = ['gs://bucket/path/*.csv'],
  skip_leading_rows = 1
);

-- Parquet external table
CREATE EXTERNAL TABLE `project.dataset.parquet_table`
OPTIONS (
  format = 'PARQUET',
  uris = ['gs://bucket/path/*.parquet']
);

8.2. Federated Query

-- Connect to Cloud SQL
SELECT * FROM EXTERNAL_QUERY(
  'projects/project/locations/us/connections/connection_id',
  'SELECT * FROM mysql_table'
);

9. Scheduled Queries

9.1. Configuration Example

-- Configure in Cloud Console or bq command
-- Run daily at 2 AM
bq query --use_legacy_sql=false \
  --schedule='every 24 hours' \
  --display_name='Daily aggregation' \
  --destination_table='project:dataset.daily_summary' \
  --replace \
  'SELECT DATE(created_at) as date, COUNT(*) as count FROM source GROUP BY 1'

10. Reference Links

• Official docs: https://cloud.google.com/bigquery/docs
• GoogleSQL reference: https://cloud.google.com/bigquery/docs/reference/standard-sql/query-syntax
• Function reference: https://cloud.google.com/bigquery/docs/reference/standard-sql/functions-all
• bq command reference: https://cloud.google.com/bigquery/docs/bq-command-line-tool
• BigQuery ML: https://cloud.google.com/bigquery/docs/bqml-introduction
• Pricing: https://cloud.google.com/bigquery/pricing