BCNF, 4NF, 5NF and Beyond: When Is 3NF Not Enough?
3NF only looks at non-key attributes, so a table whose columns are all part of a key can be in 3NF and still produce anomalies. BCNF, 4NF and 5NF close these gaps. In SQL Server we show BCNF with a signing day table and bring a lost dependency back with an indexed view, 4NF with languages and genres, the join dependency behind 5NF with a distributor table, and how 6NF relates to temporal data.
14 Nov 2026
·
17 min
·
2
