BigQuery Local Skill

Project-specific BigQuery conventions. Standard GoogleSQL syntax, bq CLI usage, JOIN patterns, window functions, BQML, and external tables are assumed knowledge.

1. Cost Guardrails

• YOU MUST: Use --dry_run before large queries
• YOU MUST: Avoid SELECT *; specify columns explicitly
• YOU MUST: Always filter on partition columns
• IMPORTANT: Partition pruning fails when functions wrap the partition column
  • Bad: WHERE DATE(created_at) = '2024-01-01'
  • Good: WHERE created_at >= '2024-01-01' AND created_at < '2024-01-02'
• IMPORTANT: Use APPROX_COUNT_DISTINCT over COUNT(DISTINCT) when exact counts are not required

2. Table Design Conventions