Database Query Skill

You have read-only access to the Gertrude PostgreSQL database for querying and analysis.

Connection Information

• •Database name: gertrude
• •User: readonly
• •Password: None required
• •Connection command: psql -U readonly -d gertrude

Database Structure

The database uses multiple schemas to organize tables:

• •parent: Parent accounts, children, computers, keychains, keys, notifications, etc.
• •child: Computer users, blocked apps, iOS devices, tokens, screenshots
• •macapp: Keystroke lines, releases, unlock requests
• •iosapp: Block groups, rules, device configurations, suspend requests
• •macos: App bundle IDs, categories, browsers, identified/unidentified apps
• •system: Deleted entities, interesting events, security events, Stripe events
• •public: Fluent migrations, jobs metadata
• •podcasts: Podcast-related tables

Common Commands

Introspect Schema

# List all tables with their schemas
psql -U readonly -d gertrude -c "\dt"

# List all schemas with privileges
psql -U readonly -d gertrude -c "\dn+"

# Describe a specific table (show columns, types, constraints)
psql -U readonly -d gertrude -c "\d parent.parents"
psql -U readonly -d gertrude -c "\d+ parent.parents"  # with more details

# List all columns in a schema
psql -U readonly -d gertrude -c "\d parent.*"

Query Data

# Run a simple query
psql -U readonly -d gertrude -c "SELECT * FROM parent.parents LIMIT 10;"

# Run a formatted query with better output
psql -U readonly -d gertrude -c "SELECT id, email, created_at FROM parent.parents ORDER BY created_at DESC LIMIT 5;"

# Count records
psql -U readonly -d gertrude -c "SELECT COUNT(*) FROM parent.parents;"

# Complex queries with joins (example)
psql -U readonly -d gertrude -c "
  SELECT p.email, COUNT(c.id) as num_children
  FROM parent.parents p
  LEFT JOIN parent.children c ON c.parent_id = p.id
  GROUP BY p.email
  LIMIT 10;
"

Format Output

# Use expanded display for wide tables
psql -U readonly -d gertrude -c "\x" -c "SELECT * FROM parent.parents LIMIT 1;"

# Export to CSV
psql -U readonly -d gertrude -c "COPY (SELECT * FROM parent.parents LIMIT 10) TO STDOUT WITH CSV HEADER;"

Workflow

1. •Understand the question: Determine what data or schema information is needed
2. •Introspect first: Use \d commands to understand table structure before writing queries
3. •Write queries: Construct appropriate SELECT queries to answer the question
4. •Analyze results: Interpret the query results and provide clear explanations
5. •Verify permissions: If you attempt any write operation, you'll get a permission error (this is expected)

Important Notes

• •Read-only access: You cannot INSERT, UPDATE, DELETE, or modify the database in any way
• •Schema qualification: Always use schema-qualified table names (e.g., parent.parents, not just parents)
• •Query carefully: Start with small LIMIT clauses to avoid overwhelming output
• •Explain results: After running queries, provide clear explanations of what the data shows

Examples

Example 1: How many parents are in the system?

psql -U readonly -d gertrude -c "SELECT COUNT(*) as total_parents FROM parent.parents;"

Example 2: What are the recent security events?

psql -U readonly -d gertrude -c "
  SELECT id, event_type, detail, created_at
  FROM system.security_events
  ORDER BY created_at DESC
  LIMIT 10;
"

Example 3: What columns are in the computers table?

psql -U readonly -d gertrude -c "\d parent.computers"