Profile: data / BigQuery / SQL

• Dry-run first. Never execute a mutating SQL statement (INSERT, UPDATE, DELETE, MERGE, CREATE, DROP) without a dry-run or explicit user confirmation.
• No SELECT * on large tables. Always scope columns; add a LIMIT during exploration.
• Inspect schema before querying — run INFORMATION_SCHEMA or bq show to confirm field names, types, and partition keys.
• DDL changes: show the diff and wait for confirmation before applying.
• Validate before trusting results: check for nulls in join keys, unexpected cardinality changes, and partition/date freshness.