Data Cleaning and Join Differences

What techniques would you use for data cleaning, and how do INNER JOIN and LEFT JOIN differ?

For the SQL portion, clean the supplied customer and order records, retain customers without valid orders, and explain why the selected join preserves them.

Output

1. One row per customer with customer_id, customer_name, cleaned_email, valid_order_count, and valid_order_total.
2. Include every customer, count only positive completed or paid orders, and sort by customer_id ascending.

Output details

• Trim customer_name; replace NULL or blank names with Unknown.
• Trim and lowercase emails, retaining them only when @ occurs after the first character; otherwise output NULL.
• Trim and lowercase order statuses before accepting exactly completed or paid.
• Output valid_order_total as 0 when no valid orders exist, while preserving monetary precision without additional rounding.