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Because several database platforms are case-insensitive and tend to convert table and field names to either uppercase (e.g. Oracle) or lowercase (e.g. PostgreSQL), we use snake_case. All names should be in lowercase.
Good
SELECT COUNT(*) AS person_count FROM person
Bad
SELECT COUNT(*) AS personCount FROM person
SELECT COUNT(*) AS Person_Count FROM person
SELECT COUNT(*) AS PERSON_COUNT FROM person