Type Errors

Solutions for data type conversion and NULL handling issues.

Common Type Conversion Errors

NULL Value Panics

Problem: Gold Digger crashes with a panic when encountering NULL values.

Error Message:

thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value'

Solution: Always cast columns to CHAR in your SQL queries:

-- ❌ Dangerous - can panic on NULL
SELECT id, name, created_at FROM users;

-- ✅ Safe - handles NULL values properly
SELECT
  CAST(id AS CHAR) as id,
  CAST(name AS CHAR) as name,
  CAST(created_at AS CHAR) as created_at
FROM users;

Non-String Type Errors

Problem: Numeric, date, or binary columns cause conversion errors.

Solution: Cast all non-string columns:

SELECT
  CAST(user_id AS CHAR) as user_id,
  username,  -- Already string, no cast needed
  CAST(balance AS CHAR) as balance,
  CAST(last_login AS CHAR) as last_login,
  CAST(is_active AS CHAR) as is_active
FROM accounts;

Best Practices for Type Safety

1. Always Use CAST

-- For all numeric types
CAST(price AS CHAR) as price,
CAST(quantity AS CHAR) as quantity,

-- For dates and timestamps
CAST(created_at AS CHAR) as created_at,
CAST(updated_at AS CHAR) as updated_at,

-- For boolean values
CAST(is_enabled AS CHAR) as is_enabled

2. Handle NULL Values Explicitly

-- Use COALESCE for default values
SELECT
  CAST(COALESCE(phone, '') AS CHAR) as phone,
  CAST(COALESCE(address, 'No address') AS CHAR) as address
FROM contacts;

3. Test Queries First

Before running large exports, test with a small subset:

-- Test with LIMIT first
SELECT CAST(id AS CHAR) as id, name
FROM large_table
LIMIT 5;

Output Format Considerations

JSON Output

NULL values in JSON output appear as null:

{
  "data": [
    {
      "id": "1",
      "name": "John",
      "phone": null
    }
  ]
}

CSV/TSV Output

NULL values in CSV/TSV appear as empty strings:

id,name,phone
1,John,
2,Jane,555-1234

Debugging Type Issues

Enable Verbose Output

gold_digger --verbose \
  --db-url "mysql://..." \
  --query "SELECT ..." \
  --output debug.json

Check Column Types

Query your database schema first:

DESCRIBE your_table;
-- or
SHOW COLUMNS FROM your_table;

Use Information Schema

SELECT
  COLUMN_NAME,
  DATA_TYPE,
  IS_NULLABLE
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = 'your_table';

Advanced Type Handling

Custom Formatting

-- Format numbers with specific precision
SELECT
  CAST(FORMAT(price, 2) AS CHAR) as price,
  CAST(FORMAT(tax_rate, 4) AS CHAR) as tax_rate
FROM products;

Date Formatting

-- Custom date formats
SELECT
  CAST(DATE_FORMAT(created_at, '%Y-%m-%d %H:%i:%s') AS CHAR) as created_at,
  CAST(DATE_FORMAT(updated_at, '%Y-%m-%d') AS CHAR) as updated_date
FROM records;

When to Contact Support

If you continue experiencing type errors after following these guidelines:

1. Provide the exact SQL query causing issues
2. Include the table schema (DESCRIBE table_name)
3. Share the complete error message
4. Specify which output format you're using