Structured Logging

SQLite for Structured Data

Decision Check

Before writing any data analysis code, evaluate:

1. Will the data be queried more than once? -> Use SQLite
2. Are GROUP BY, COUNT, AVG, or JOIN operations needed? -> Use SQLite
3. Is custom Python/jq parsing code about to be written? -> Use SQLite instead
4. Is the dataset >100 records? -> Use SQLite

If the answer to any question above is YES, use SQLite. Do not write custom parsing code.

# Custom code for every query:
cat data.json | jq '.[] | select(.status=="failed")' | jq -r '.error_type' | sort | uniq -c

# SQL does the work:
sqlite3 data.db "SELECT error_type, COUNT(*) FROM errors WHERE status='failed' GROUP BY error_type"

Core Principle

SQLite is just a file -- no server, no setup, zero dependencies. Apply it when custom parsing code would otherwise be written or data would be re-processed for each query.

When to Use SQLite

Apply when ANY of these conditions hold:

• >100 records -- JSON/grep becomes unwieldy
• Multiple aggregations -- GROUP BY, COUNT, AVG needed
• Multiple queries -- Follow-up questions about the same data are expected
• Correlation needed -- Joining data from multiple sources
• State tracking -- Queryable progress/status over time is needed

When NOT to Use SQLite

Skip SQLite when ALL of these are true:

• <50 records total
• Single simple query
• No aggregations needed
• No follow-up questions expected

For tiny datasets with simple access, JSON/grep is fine.

Red Flags -- Use SQLite Instead

STOP and use SQLite when about to:

• Write Python/Node code to parse JSON/CSV for analysis
• Run the same jq/grep command with slight variations
• Write custom aggregation logic (COUNT, AVG, GROUP BY in code)
• Manually correlate data by timestamps or IDs
• Create temp files to store intermediate results
• Process the same data multiple times for different questions

All of these mean: Load into SQLite once, query with SQL.

The Threshold

Rule of thumb: If parsing code is being written or data is being re-processed, use SQLite instead.

Available Tools

sqlite3 (always available)

sqlite3 ~/.claude-logs/project.db

sqlite-utils (optional, simplifies import)

Check availability before use:

command -v sqlite-utils >/dev/null 2>&1 && echo "available" || echo "not installed"

If sqlite-utils is available:

sqlite-utils insert data.db table_name data.json --pk=id
sqlite-utils query data.db "SELECT * FROM table"

If sqlite-utils is NOT available, fall back to sqlite3 with manual import:

sqlite3 data.db <<EOF
CREATE TABLE IF NOT EXISTS results (status TEXT, error_message TEXT);
.mode json
.import data.json results
EOF

Alternatively, install sqlite-utils: uv tool install sqlite-utils

Quick Start

Store Location

~/.claude-logs/<project-name>.db  # Persists across sessions

Basic Workflow

# 1. Connect
PROJECT=$(basename $(git rev-parse --show-toplevel 2>/dev/null || pwd))
sqlite3 ~/.claude-logs/$PROJECT.db

# 2. Create table (first time)
CREATE TABLE results (
  id INTEGER PRIMARY KEY,
  name TEXT,
  status TEXT,
  duration_ms INTEGER
);

# 3. Load data
INSERT INTO results (name, status, duration_ms)
SELECT json_extract(value, '$.name'),
       json_extract(value, '$.status'),
       json_extract(value, '$.duration_ms')
FROM json_each(readfile('data.json'));

# 4. Query (SQL does the work)
SELECT status, COUNT(*), AVG(duration_ms)
FROM results
GROUP BY status;

Key Mindset Shift

From: "Process data once and done" To: "Make data queryable"

Benefits:

• Follow-up questions require no re-processing -- data is already loaded
• Different analyses run instantly against the same dataset
• State persists across sessions
• SQL handles complexity -- less custom code needed

Additional Resources

• ./references/patterns.md -- Python vs SQL side-by-side comparison and real-world examples (test analysis, error correlation, file processing state)

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