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# DuckDB Function Patterns

User-defined functions and stored procedures.

## Validation Function Pattern

```sql
CREATE OR REPLACE FUNCTION validate_checksum(sentence TEXT)
RETURNS BOOLEAN
AS $$
    SELECT 
        CASE 
            WHEN sentence LIKE '%*__' THEN
                -- Extract data and checksum
                TRUE  -- Implement actual XOR validation
            ELSE FALSE
        END;
$$;
```

## Insert Function Pattern

```sql
CREATE OR REPLACE FUNCTION insert_sensor_data(sentence TEXT)
RETURNS UUID
AS $$
DECLARE
    record_id_val UUID;
    checksum_valid_val BOOLEAN;
BEGIN
    -- Validate sentence
    checksum_valid_val := validate_checksum(sentence);
    
    -- Insert record
    INSERT INTO sensor_data (
        original_sentence,
        checksum_valid,
        -- ... parse fields from sentence
    ) VALUES (
        sentence,
        checksum_valid_val,
        -- ... values
    )
    RETURNING record_id INTO record_id_val;
    
    RETURN record_id_val;
END;
$$;
```

## Maintenance Procedure Pattern

```sql
CREATE OR REPLACE PROCEDURE cleanup_old_records(days_to_keep INTEGER)
AS $$
BEGIN
    DELETE FROM raw_lines
    WHERE received_at < current_timestamp - INTERVAL '1' DAY * days_to_keep;
    
    VACUUM;
    ANALYZE;
END;
$$;

-- Run cleanup
CALL cleanup_old_records(90);
```

## Related Documents

- [Schema Patterns](schemas.md)
- [Constraints](constraints.md)
- [Views](views.md)

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