First normal form

📘What it really is

• A table is in first normal form (1NF) when:
• each column holds one value (no lists like "Pen, Notebook, Bag");
• there are no repeating groups of columns (phone1, phone2, phone3);

• each row is unique (it has a primary key).

• Fixing violations:

• a list in a column becomes rows in another table (order_items instead of product_names);
• repeating columns become rows in a child table (customer_phones with one phone per row), or you decide only one is really needed.

• Why it matters: you can't search, count, join or constrain values hidden inside lists. "How many orders included pens?" becomes text-matching guesswork.

• PostgreSQL's array and jsonb columns can hold lists; use them for genuinely self-contained data (like a list of tags you only ever show), not for things you'll query, count or link.