MYSQL Sum: How to excludes all instances either one of two other columns are null

You can do it with conditional aggregation:

SELECT customer_id,
       SUM(CASE WHEN blocked IS NULL AND unapproved IS NULL THEN cost ELSE 0 END) total
FROM tablename
GROUP BY customer_id;

Or:

SELECT customer_id,
       SUM(CASE WHEN COALESCE(locked, unapproved) IS NULL THEN cost ELSE 0 END) total
FROM tablename
GROUP BY customer_id;

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