First Normal Form (1NF)

Concepts: dmFirstNormalForm

1NF: No Lists in Cells A table is in first normal form when every cell contains a single atomic value. No comma-separated lists. No arrays stored as strings. No multiple values crammed into one column. This sounds obvious, but 1NF violations are everywhere in real data. A tags column with 'python, sql, spark'. A phone_numbers column with '555-1234, 555-5678'. These break filtering, indexing, and joining. Here is a 1NF violation: You cannot filter for 'students taking Physics' without string parsing. You cannot count courses per student without splitting on commas. You cannot join to a courses table because the FK is a comma-separated string, not a single value. The fix: one row per student-course combination.